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Edit File : sre_parse.py \| Size : 39.82 KB
# # Secret Labs' Regular Expression Engine # # convert re-style regular expression to sre pattern # # Copyright (c) 1998-2001 by Secret Labs AB. All rights reserved. # # See the sre.py file for information on usage and redistribution. # """Internal support module for sre""" # XXX: show string offset and offending character for all errors from sre_constants import * SPECIAL_CHARS = ".\\[{()+?^$\|" REPEAT_CHARS = "+?{" DIGITS = frozenset("0123456789") OCTDIGITS = frozenset("01234567") HEXDIGITS = frozenset("0123456789abcdefABCDEF") ASCIILETTERS = frozenset("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ") WHITESPACE = frozenset(" \t\n\r\v\f") _REPEATCODES = frozenset({MIN_REPEAT, MAX_REPEAT}) _UNITCODES = frozenset({ANY, RANGE, IN, LITERAL, NOT_LITERAL, CATEGORY}) ESCAPES = { r"\a": (LITERAL, ord("\a")), r"\b": (LITERAL, ord("\b")), r"\f": (LITERAL, ord("\f")), r"\n": (LITERAL, ord("\n")), r"\r": (LITERAL, ord("\r")), r"\t": (LITERAL, ord("\t")), r"\v": (LITERAL, ord("\v")), r"\\": (LITERAL, ord("\\")) } CATEGORIES = { r"\A": (AT, AT_BEGINNING_STRING), # start of string r"\b": (AT, AT_BOUNDARY), r"\B": (AT, AT_NON_BOUNDARY), r"\d": (IN, [(CATEGORY, CATEGORY_DIGIT)]), r"\D": (IN, [(CATEGORY, CATEGORY_NOT_DIGIT)]), r"\s": (IN, [(CATEGORY, CATEGORY_SPACE)]), r"\S": (IN, [(CATEGORY, CATEGORY_NOT_SPACE)]), r"\w": (IN, [(CATEGORY, CATEGORY_WORD)]), r"\W": (IN, [(CATEGORY, CATEGORY_NOT_WORD)]), r"\Z": (AT, AT_END_STRING), # end of string } FLAGS = { # standard flags "i": SRE_FLAG_IGNORECASE, "L": SRE_FLAG_LOCALE, "m": SRE_FLAG_MULTILINE, "s": SRE_FLAG_DOTALL, "x": SRE_FLAG_VERBOSE, # extensions "a": SRE_FLAG_ASCII, "t": SRE_FLAG_TEMPLATE, "u": SRE_FLAG_UNICODE, } TYPE_FLAGS = SRE_FLAG_ASCII \| SRE_FLAG_LOCALE \| SRE_FLAG_UNICODE GLOBAL_FLAGS = SRE_FLAG_DEBUG \| SRE_FLAG_TEMPLATE class Verbose(Exception): pass class State: # keeps track of state for parsing def __init__(self): self.flags = 0 self.groupdict = {} self.groupwidths = [None] # group 0 self.lookbehindgroups = None self.grouprefpos = {} @property def groups(self): return len(self.groupwidths) def opengroup(self, name=None): gid = self.groups self.groupwidths.append(None) if self.groups > MAXGROUPS: raise error("too many groups") if name is not None: ogid = self.groupdict.get(name, None) if ogid is not None: raise error("redefinition of group name %r as group %d; " "was group %d" % (name, gid, ogid)) self.groupdict[name] = gid return gid def closegroup(self, gid, p): self.groupwidths[gid] = p.getwidth() def checkgroup(self, gid): return gid < self.groups and self.groupwidths[gid] is not None def checklookbehindgroup(self, gid, source): if self.lookbehindgroups is not None: if not self.checkgroup(gid): raise source.error('cannot refer to an open group') if gid >= self.lookbehindgroups: raise source.error('cannot refer to group defined in the same ' 'lookbehind subpattern') class SubPattern: # a subpattern, in intermediate form def __init__(self, state, data=None): self.state = state if data is None: data = [] self.data = data self.width = None def dump(self, level=0): nl = True seqtypes = (tuple, list) for op, av in self.data: print(level" " + str(op), end='') if op is IN: # member sublanguage print() for op, a in av: print((level+1)" " + str(op), a) elif op is BRANCH: print() for i, a in enumerate(av[1]): if i: print(level" " + "OR") a.dump(level+1) elif op is GROUPREF_EXISTS: condgroup, item_yes, item_no = av print('', condgroup) item_yes.dump(level+1) if item_no: print(level" " + "ELSE") item_no.dump(level+1) elif isinstance(av, seqtypes): nl = False for a in av: if isinstance(a, SubPattern): if not nl: print() a.dump(level+1) nl = True else: if not nl: print(' ', end='') print(a, end='') nl = False if not nl: print() else: print('', av) def __repr__(self): return repr(self.data) def __len__(self): return len(self.data) def __delitem__(self, index): del self.data[index] def __getitem__(self, index): if isinstance(index, slice): return SubPattern(self.state, self.data[index]) return self.data[index] def __setitem__(self, index, code): self.data[index] = code def insert(self, index, code): self.data.insert(index, code) def append(self, code): self.data.append(code) def getwidth(self): # determine the width (min, max) for this subpattern if self.width is not None: return self.width lo = hi = 0 for op, av in self.data: if op is BRANCH: i = MAXREPEAT - 1 j = 0 for av in av[1]: l, h = av.getwidth() i = min(i, l) j = max(j, h) lo = lo + i hi = hi + j elif op is CALL: i, j = av.getwidth() lo = lo + i hi = hi + j elif op is SUBPATTERN: i, j = av[-1].getwidth() lo = lo + i hi = hi + j elif op in _REPEATCODES: i, j = av[2].getwidth() lo = lo + i * av[0] hi = hi + j * av[1] elif op in _UNITCODES: lo = lo + 1 hi = hi + 1 elif op is GROUPREF: i, j = self.state.groupwidths[av] lo = lo + i hi = hi + j elif op is GROUPREF_EXISTS: i, j = av[1].getwidth() if av[2] is not None: l, h = av[2].getwidth() i = min(i, l) j = max(j, h) else: i = 0 lo = lo + i hi = hi + j elif op is SUCCESS: break self.width = min(lo, MAXREPEAT - 1), min(hi, MAXREPEAT) return self.width class Tokenizer: def __init__(self, string): self.istext = isinstance(string, str) self.string = string if not self.istext: string = str(string, 'latin1') self.decoded_string = string self.index = 0 self.next = None self.__next() def __next(self): index = self.index try: char = self.decoded_string[index] except IndexError: self.next = None return if char == "\\": index += 1 try: char += self.decoded_string[index] except IndexError: raise error("bad escape (end of pattern)", self.string, len(self.string) - 1) from None self.index = index + 1 self.next = char def match(self, char): if char == self.next: self.__next() return True return False def get(self): this = self.next self.__next() return this def getwhile(self, n, charset): result = '' for _ in range(n): c = self.next if c not in charset: break result += c self.__next() return result def getuntil(self, terminator, name): result = '' while True: c = self.next self.__next() if c is None: if not result: raise self.error("missing " + name) raise self.error("missing %s, unterminated name" % terminator, len(result)) if c == terminator: if not result: raise self.error("missing " + name, 1) break result += c return result @property def pos(self): return self.index - len(self.next or '') def tell(self): return self.index - len(self.next or '') def seek(self, index): self.index = index self.__next() def error(self, msg, offset=0): return error(msg, self.string, self.tell() - offset) def _class_escape(source, escape): # handle escape code inside character class code = ESCAPES.get(escape) if code: return code code = CATEGORIES.get(escape) if code and code[0] is IN: return code try: c = escape[1:2] if c == "x": # hexadecimal escape (exactly two digits) escape += source.getwhile(2, HEXDIGITS) if len(escape) != 4: raise source.error("incomplete escape %s" % escape, len(escape)) return LITERAL, int(escape[2:], 16) elif c == "u" and source.istext: # unicode escape (exactly four digits) escape += source.getwhile(4, HEXDIGITS) if len(escape) != 6: raise source.error("incomplete escape %s" % escape, len(escape)) return LITERAL, int(escape[2:], 16) elif c == "U" and source.istext: # unicode escape (exactly eight digits) escape += source.getwhile(8, HEXDIGITS) if len(escape) != 10: raise source.error("incomplete escape %s" % escape, len(escape)) c = int(escape[2:], 16) chr(c) # raise ValueError for invalid code return LITERAL, c elif c == "N" and source.istext: import unicodedata # named unicode escape e.g. \N{EM DASH} if not source.match('{'): raise source.error("missing {") charname = source.getuntil('}', 'character name') try: c = ord(unicodedata.lookup(charname)) except (KeyError, TypeError): raise source.error("undefined character name %r" % charname, len(charname) + len(r'\N{}')) return LITERAL, c elif c in OCTDIGITS: # octal escape (up to three digits) escape += source.getwhile(2, OCTDIGITS) c = int(escape[1:], 8) if c > 0o377: raise source.error('octal escape value %s outside of ' 'range 0-0o377' % escape, len(escape)) return LITERAL, c elif c in DIGITS: raise ValueError if len(escape) == 2: if c in ASCIILETTERS: raise source.error('bad escape %s' % escape, len(escape)) return LITERAL, ord(escape[1]) except ValueError: pass raise source.error("bad escape %s" % escape, len(escape)) def _escape(source, escape, state): # handle escape code in expression code = CATEGORIES.get(escape) if code: return code code = ESCAPES.get(escape) if code: return code try: c = escape[1:2] if c == "x": # hexadecimal escape escape += source.getwhile(2, HEXDIGITS) if len(escape) != 4: raise source.error("incomplete escape %s" % escape, len(escape)) return LITERAL, int(escape[2:], 16) elif c == "u" and source.istext: # unicode escape (exactly four digits) escape += source.getwhile(4, HEXDIGITS) if len(escape) != 6: raise source.error("incomplete escape %s" % escape, len(escape)) return LITERAL, int(escape[2:], 16) elif c == "U" and source.istext: # unicode escape (exactly eight digits) escape += source.getwhile(8, HEXDIGITS) if len(escape) != 10: raise source.error("incomplete escape %s" % escape, len(escape)) c = int(escape[2:], 16) chr(c) # raise ValueError for invalid code return LITERAL, c elif c == "N" and source.istext: import unicodedata # named unicode escape e.g. \N{EM DASH} if not source.match('{'): raise source.error("missing {") charname = source.getuntil('}', 'character name') try: c = ord(unicodedata.lookup(charname)) except (KeyError, TypeError): raise source.error("undefined character name %r" % charname, len(charname) + len(r'\N{}')) return LITERAL, c elif c == "0": # octal escape escape += source.getwhile(2, OCTDIGITS) return LITERAL, int(escape[1:], 8) elif c in DIGITS: # octal escape or decimal group reference (sigh) if source.next in DIGITS: escape += source.get() if (escape[1] in OCTDIGITS and escape[2] in OCTDIGITS and source.next in OCTDIGITS): # got three octal digits; this is an octal escape escape += source.get() c = int(escape[1:], 8) if c > 0o377: raise source.error('octal escape value %s outside of ' 'range 0-0o377' % escape, len(escape)) return LITERAL, c # not an octal escape, so this is a group reference group = int(escape[1:]) if group < state.groups: if not state.checkgroup(group): raise source.error("cannot refer to an open group", len(escape)) state.checklookbehindgroup(group, source) return GROUPREF, group raise source.error("invalid group reference %d" % group, len(escape) - 1) if len(escape) == 2: if c in ASCIILETTERS: raise source.error("bad escape %s" % escape, len(escape)) return LITERAL, ord(escape[1]) except ValueError: pass raise source.error("bad escape %s" % escape, len(escape)) def _uniq(items): return list(dict.fromkeys(items)) def _parse_sub(source, state, verbose, nested): # parse an alternation: a\|b\|c items = [] itemsappend = items.append sourcematch = source.match start = source.tell() while True: itemsappend(_parse(source, state, verbose, nested + 1, not nested and not items)) if not sourcematch("\|"): break if len(items) == 1: return items[0] subpattern = SubPattern(state) # check if all items share a common prefix while True: prefix = None for item in items: if not item: break if prefix is None: prefix = item[0] elif item[0] != prefix: break else: # all subitems start with a common "prefix". # move it out of the branch for item in items: del item[0] subpattern.append(prefix) continue # check next one break # check if the branch can be replaced by a character set set = [] for item in items: if len(item) != 1: break op, av = item[0] if op is LITERAL: set.append((op, av)) elif op is IN and av[0][0] is not NEGATE: set.extend(av) else: break else: # we can store this as a character set instead of a # branch (the compiler may optimize this even more) subpattern.append((IN, _uniq(set))) return subpattern subpattern.append((BRANCH, (None, items))) return subpattern def _parse(source, state, verbose, nested, first=False): # parse a simple pattern subpattern = SubPattern(state) # precompute constants into local variables subpatternappend = subpattern.append sourceget = source.get sourcematch = source.match _len = len _ord = ord while True: this = source.next if this is None: break # end of pattern if this in "\|)": break # end of subpattern sourceget() if verbose: # skip whitespace and comments if this in WHITESPACE: continue if this == "#": while True: this = sourceget() if this is None or this == "\n": break continue if this[0] == "\\": code = _escape(source, this, state) subpatternappend(code) elif this not in SPECIAL_CHARS: subpatternappend((LITERAL, _ord(this))) elif this == "[": here = source.tell() - 1 # character set set = [] setappend = set.append ## if sourcematch(":"): ## pass # handle character classes if source.next == '[': import warnings warnings.warn( 'Possible nested set at position %d' % source.tell(), FutureWarning, stacklevel=nested + 6 ) negate = sourcematch("^") # check remaining characters while True: this = sourceget() if this is None: raise source.error("unterminated character set", source.tell() - here) if this == "]" and set: break elif this[0] == "\\": code1 = _class_escape(source, this) else: if set and this in '-&~\|' and source.next == this: import warnings warnings.warn( 'Possible set %s at position %d' % ( 'difference' if this == '-' else 'intersection' if this == '&' else 'symmetric difference' if this == '~' else 'union', source.tell() - 1), FutureWarning, stacklevel=nested + 6 ) code1 = LITERAL, _ord(this) if sourcematch("-"): # potential range that = sourceget() if that is None: raise source.error("unterminated character set", source.tell() - here) if that == "]": if code1[0] is IN: code1 = code1[1][0] setappend(code1) setappend((LITERAL, _ord("-"))) break if that[0] == "\\": code2 = _class_escape(source, that) else: if that == '-': import warnings warnings.warn( 'Possible set difference at position %d' % ( source.tell() - 2), FutureWarning, stacklevel=nested + 6 ) code2 = LITERAL, _ord(that) if code1[0] != LITERAL or code2[0] != LITERAL: msg = "bad character range %s-%s" % (this, that) raise source.error(msg, len(this) + 1 + len(that)) lo = code1[1] hi = code2[1] if hi < lo: msg = "bad character range %s-%s" % (this, that) raise source.error(msg, len(this) + 1 + len(that)) setappend((RANGE, (lo, hi))) else: if code1[0] is IN: code1 = code1[1][0] setappend(code1) set = _uniq(set) # XXX: <fl> should move set optimization to compiler! if _len(set) == 1 and set[0][0] is LITERAL: # optimization if negate: subpatternappend((NOT_LITERAL, set[0][1])) else: subpatternappend(set[0]) else: if negate: set.insert(0, (NEGATE, None)) # charmap optimization can't be added here because # global flags still are not known subpatternappend((IN, set)) elif this in REPEAT_CHARS: # repeat previous item here = source.tell() if this == "?": min, max = 0, 1 elif this == "*": min, max = 0, MAXREPEAT elif this == "+": min, max = 1, MAXREPEAT elif this == "{": if source.next == "}": subpatternappend((LITERAL, _ord(this))) continue min, max = 0, MAXREPEAT lo = hi = "" while source.next in DIGITS: lo += sourceget() if sourcematch(","): while source.next in DIGITS: hi += sourceget() else: hi = lo if not sourcematch("}"): subpatternappend((LITERAL, _ord(this))) source.seek(here) continue if lo: min = int(lo) if min >= MAXREPEAT: raise OverflowError("the repetition number is too large") if hi: max = int(hi) if max >= MAXREPEAT: raise OverflowError("the repetition number is too large") if max < min: raise source.error("min repeat greater than max repeat", source.tell() - here) else: raise AssertionError("unsupported quantifier %r" % (char,)) # figure out which item to repeat if subpattern: item = subpattern[-1:] else: item = None if not item or item[0][0] is AT: raise source.error("nothing to repeat", source.tell() - here + len(this)) if item[0][0] in _REPEATCODES: raise source.error("multiple repeat", source.tell() - here + len(this)) if item[0][0] is SUBPATTERN: group, add_flags, del_flags, p = item[0][1] if group is None and not add_flags and not del_flags: item = p if sourcematch("?"): subpattern[-1] = (MIN_REPEAT, (min, max, item)) else: subpattern[-1] = (MAX_REPEAT, (min, max, item)) elif this == ".": subpatternappend((ANY, None)) elif this == "(": start = source.tell() - 1 group = True name = None add_flags = 0 del_flags = 0 if sourcematch("?"): # options char = sourceget() if char is None: raise source.error("unexpected end of pattern") if char == "P": # python extensions if sourcematch("<"): # named group: skip forward to end of name name = source.getuntil(">", "group name") if not name.isidentifier(): msg = "bad character in group name %r" % name raise source.error(msg, len(name) + 1) elif sourcematch("="): # named backreference name = source.getuntil(")", "group name") if not name.isidentifier(): msg = "bad character in group name %r" % name raise source.error(msg, len(name) + 1) gid = state.groupdict.get(name) if gid is None: msg = "unknown group name %r" % name raise source.error(msg, len(name) + 1) if not state.checkgroup(gid): raise source.error("cannot refer to an open group", len(name) + 1) state.checklookbehindgroup(gid, source) subpatternappend((GROUPREF, gid)) continue else: char = sourceget() if char is None: raise source.error("unexpected end of pattern") raise source.error("unknown extension ?P" + char, len(char) + 2) elif char == ":": # non-capturing group group = None elif char == "#": # comment while True: if source.next is None: raise source.error("missing ), unterminated comment", source.tell() - start) if sourceget() == ")": break continue elif char in "=!<": # lookahead assertions dir = 1 if char == "<": char = sourceget() if char is None: raise source.error("unexpected end of pattern") if char not in "=!": raise source.error("unknown extension ?<" + char, len(char) + 2) dir = -1 # lookbehind lookbehindgroups = state.lookbehindgroups if lookbehindgroups is None: state.lookbehindgroups = state.groups p = _parse_sub(source, state, verbose, nested + 1) if dir < 0: if lookbehindgroups is None: state.lookbehindgroups = None if not sourcematch(")"): raise source.error("missing ), unterminated subpattern", source.tell() - start) if char == "=": subpatternappend((ASSERT, (dir, p))) else: subpatternappend((ASSERT_NOT, (dir, p))) continue elif char == "(": # conditional backreference group condname = source.getuntil(")", "group name") if condname.isidentifier(): condgroup = state.groupdict.get(condname) if condgroup is None: msg = "unknown group name %r" % condname raise source.error(msg, len(condname) + 1) else: try: condgroup = int(condname) if condgroup < 0: raise ValueError except ValueError: msg = "bad character in group name %r" % condname raise source.error(msg, len(condname) + 1) from None if not condgroup: raise source.error("bad group number", len(condname) + 1) if condgroup >= MAXGROUPS: msg = "invalid group reference %d" % condgroup raise source.error(msg, len(condname) + 1) if condgroup not in state.grouprefpos: state.grouprefpos[condgroup] = ( source.tell() - len(condname) - 1 ) state.checklookbehindgroup(condgroup, source) item_yes = _parse(source, state, verbose, nested + 1) if source.match("\|"): item_no = _parse(source, state, verbose, nested + 1) if source.next == "\|": raise source.error("conditional backref with more than two branches") else: item_no = None if not source.match(")"): raise source.error("missing ), unterminated subpattern", source.tell() - start) subpatternappend((GROUPREF_EXISTS, (condgroup, item_yes, item_no))) continue elif char in FLAGS or char == "-": # flags flags = _parse_flags(source, state, char) if flags is None: # global flags if not first or subpattern: import warnings warnings.warn( 'Flags not at the start of the expression %r%s' ' but at position %d' % ( source.string[:20], # truncate long regexes ' (truncated)' if len(source.string) > 20 else '', start, ), DeprecationWarning, stacklevel=nested + 6 ) if (state.flags & SRE_FLAG_VERBOSE) and not verbose: raise Verbose continue add_flags, del_flags = flags group = None else: raise source.error("unknown extension ?" + char, len(char) + 1) # parse group contents if group is not None: try: group = state.opengroup(name) except error as err: raise source.error(err.msg, len(name) + 1) from None sub_verbose = ((verbose or (add_flags & SRE_FLAG_VERBOSE)) and not (del_flags & SRE_FLAG_VERBOSE)) p = _parse_sub(source, state, sub_verbose, nested + 1) if not source.match(")"): raise source.error("missing ), unterminated subpattern", source.tell() - start) if group is not None: state.closegroup(group, p) subpatternappend((SUBPATTERN, (group, add_flags, del_flags, p))) elif this == "^": subpatternappend((AT, AT_BEGINNING)) elif this == "$": subpatternappend((AT, AT_END)) else: raise AssertionError("unsupported special character %r" % (char,)) # unpack non-capturing groups for i in range(len(subpattern))[::-1]: op, av = subpattern[i] if op is SUBPATTERN: group, add_flags, del_flags, p = av if group is None and not add_flags and not del_flags: subpattern[i: i+1] = p return subpattern def _parse_flags(source, state, char): sourceget = source.get add_flags = 0 del_flags = 0 if char != "-": while True: flag = FLAGS[char] if source.istext: if char == 'L': msg = "bad inline flags: cannot use 'L' flag with a str pattern" raise source.error(msg) else: if char == 'u': msg = "bad inline flags: cannot use 'u' flag with a bytes pattern" raise source.error(msg) add_flags \|= flag if (flag & TYPE_FLAGS) and (add_flags & TYPE_FLAGS) != flag: msg = "bad inline flags: flags 'a', 'u' and 'L' are incompatible" raise source.error(msg) char = sourceget() if char is None: raise source.error("missing -, : or )") if char in ")-:": break if char not in FLAGS: msg = "unknown flag" if char.isalpha() else "missing -, : or )" raise source.error(msg, len(char)) if char == ")": state.flags \|= add_flags return None if add_flags & GLOBAL_FLAGS: raise source.error("bad inline flags: cannot turn on global flag", 1) if char == "-": char = sourceget() if char is None: raise source.error("missing flag") if char not in FLAGS: msg = "unknown flag" if char.isalpha() else "missing flag" raise source.error(msg, len(char)) while True: flag = FLAGS[char] if flag & TYPE_FLAGS: msg = "bad inline flags: cannot turn off flags 'a', 'u' and 'L'" raise source.error(msg) del_flags \|= flag char = sourceget() if char is None: raise source.error("missing :") if char == ":": break if char not in FLAGS: msg = "unknown flag" if char.isalpha() else "missing :" raise source.error(msg, len(char)) assert char == ":" if del_flags & GLOBAL_FLAGS: raise source.error("bad inline flags: cannot turn off global flag", 1) if add_flags & del_flags: raise source.error("bad inline flags: flag turned on and off", 1) return add_flags, del_flags def fix_flags(src, flags): # Check and fix flags according to the type of pattern (str or bytes) if isinstance(src, str): if flags & SRE_FLAG_LOCALE: raise ValueError("cannot use LOCALE flag with a str pattern") if not flags & SRE_FLAG_ASCII: flags \|= SRE_FLAG_UNICODE elif flags & SRE_FLAG_UNICODE: raise ValueError("ASCII and UNICODE flags are incompatible") else: if flags & SRE_FLAG_UNICODE: raise ValueError("cannot use UNICODE flag with a bytes pattern") if flags & SRE_FLAG_LOCALE and flags & SRE_FLAG_ASCII: raise ValueError("ASCII and LOCALE flags are incompatible") return flags def parse(str, flags=0, state=None): # parse 're' pattern into list of (opcode, argument) tuples source = Tokenizer(str) if state is None: state = State() state.flags = flags state.str = str try: p = _parse_sub(source, state, flags & SRE_FLAG_VERBOSE, 0) except Verbose: # the VERBOSE flag was switched on inside the pattern. to be # on the safe side, we'll parse the whole thing again... state = State() state.flags = flags \| SRE_FLAG_VERBOSE state.str = str source.seek(0) p = _parse_sub(source, state, True, 0) p.state.flags = fix_flags(str, p.state.flags) if source.next is not None: assert source.next == ")" raise source.error("unbalanced parenthesis") for g in p.state.grouprefpos: if g >= p.state.groups: msg = "invalid group reference %d" % g raise error(msg, str, p.state.grouprefpos[g]) if flags & SRE_FLAG_DEBUG: p.dump() return p def parse_template(source, state): # parse 're' replacement string into list of literals and # group references s = Tokenizer(source) sget = s.get groups = [] literals = [] literal = [] lappend = literal.append def addgroup(index, pos): if index > state.groups: raise s.error("invalid group reference %d" % index, pos) if literal: literals.append(''.join(literal)) del literal[:] groups.append((len(literals), index)) literals.append(None) groupindex = state.groupindex while True: this = sget() if this is None: break # end of replacement string if this[0] == "\\": # group c = this[1] if c == "g": name = "" if not s.match("<"): raise s.error("missing <") name = s.getuntil(">", "group name") if name.isidentifier(): try: index = groupindex[name] except KeyError: raise IndexError("unknown group name %r" % name) else: try: index = int(name) if index < 0: raise ValueError except ValueError: raise s.error("bad character in group name %r" % name, len(name) + 1) from None if index >= MAXGROUPS: raise s.error("invalid group reference %d" % index, len(name) + 1) addgroup(index, len(name) + 1) elif c == "0": if s.next in OCTDIGITS: this += sget() if s.next in OCTDIGITS: this += sget() lappend(chr(int(this[1:], 8) & 0xff)) elif c in DIGITS: isoctal = False if s.next in DIGITS: this += sget() if (c in OCTDIGITS and this[2] in OCTDIGITS and s.next in OCTDIGITS): this += sget() isoctal = True c = int(this[1:], 8) if c > 0o377: raise s.error('octal escape value %s outside of ' 'range 0-0o377' % this, len(this)) lappend(chr(c)) if not isoctal: addgroup(int(this[1:]), len(this) - 1) else: try: this = chr(ESCAPES[this][1]) except KeyError: if c in ASCIILETTERS: raise s.error('bad escape %s' % this, len(this)) lappend(this) else: lappend(this) if literal: literals.append(''.join(literal)) if not isinstance(source, str): # The tokenizer implicitly decodes bytes objects as latin-1, we must # therefore re-encode the final representation. literals = [None if s is None else s.encode('latin-1') for s in literals] return groups, literals def expand_template(template, match): g = match.group empty = match.string[:0] groups, literals = template literals = literals[:] try: for index, group in groups: literals[index] = g(group) or empty except IndexError: raise error("invalid group reference %d" % index) return empty.join(literals) Back

Edit File : sre_parse.py | Size : 39.82 KB

#
# Secret Labs' Regular Expression Engine
#
# convert re-style regular expression to sre pattern
#
# Copyright (c) 1998-2001 by Secret Labs AB.  All rights reserved.
#
# See the sre.py file for information on usage and redistribution.
#

"""Internal support module for sre"""

# XXX: show string offset and offending character for all errors

from sre_constants import *

SPECIAL_CHARS = ".\\[{()*+?^$|"
REPEAT_CHARS = "*+?{"

DIGITS = frozenset("0123456789")

OCTDIGITS = frozenset("01234567")
HEXDIGITS = frozenset("0123456789abcdefABCDEF")
ASCIILETTERS = frozenset("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")

WHITESPACE = frozenset(" \t\n\r\v\f")

_REPEATCODES = frozenset({MIN_REPEAT, MAX_REPEAT})
_UNITCODES = frozenset({ANY, RANGE, IN, LITERAL, NOT_LITERAL, CATEGORY})

ESCAPES = {
    r"\a": (LITERAL, ord("\a")),
    r"\b": (LITERAL, ord("\b")),
    r"\f": (LITERAL, ord("\f")),
    r"\n": (LITERAL, ord("\n")),
    r"\r": (LITERAL, ord("\r")),
    r"\t": (LITERAL, ord("\t")),
    r"\v": (LITERAL, ord("\v")),
    r"\\": (LITERAL, ord("\\"))
}

CATEGORIES = {
    r"\A": (AT, AT_BEGINNING_STRING), # start of string
    r"\b": (AT, AT_BOUNDARY),
    r"\B": (AT, AT_NON_BOUNDARY),
    r"\d": (IN, [(CATEGORY, CATEGORY_DIGIT)]),
    r"\D": (IN, [(CATEGORY, CATEGORY_NOT_DIGIT)]),
    r"\s": (IN, [(CATEGORY, CATEGORY_SPACE)]),
    r"\S": (IN, [(CATEGORY, CATEGORY_NOT_SPACE)]),
    r"\w": (IN, [(CATEGORY, CATEGORY_WORD)]),
    r"\W": (IN, [(CATEGORY, CATEGORY_NOT_WORD)]),
    r"\Z": (AT, AT_END_STRING), # end of string
}

FLAGS = {
    # standard flags
    "i": SRE_FLAG_IGNORECASE,
    "L": SRE_FLAG_LOCALE,
    "m": SRE_FLAG_MULTILINE,
    "s": SRE_FLAG_DOTALL,
    "x": SRE_FLAG_VERBOSE,
    # extensions
    "a": SRE_FLAG_ASCII,
    "t": SRE_FLAG_TEMPLATE,
    "u": SRE_FLAG_UNICODE,
}

TYPE_FLAGS = SRE_FLAG_ASCII | SRE_FLAG_LOCALE | SRE_FLAG_UNICODE
GLOBAL_FLAGS = SRE_FLAG_DEBUG | SRE_FLAG_TEMPLATE

class Verbose(Exception):
    pass

class State:
    # keeps track of state for parsing
    def __init__(self):
        self.flags = 0
        self.groupdict = {}
        self.groupwidths = [None]  # group 0
        self.lookbehindgroups = None
        self.grouprefpos = {}
    @property
    def groups(self):
        return len(self.groupwidths)
    def opengroup(self, name=None):
        gid = self.groups
        self.groupwidths.append(None)
        if self.groups > MAXGROUPS:
            raise error("too many groups")
        if name is not None:
            ogid = self.groupdict.get(name, None)
            if ogid is not None:
                raise error("redefinition of group name %r as group %d; "
                            "was group %d" % (name, gid,  ogid))
            self.groupdict[name] = gid
        return gid
    def closegroup(self, gid, p):
        self.groupwidths[gid] = p.getwidth()
    def checkgroup(self, gid):
        return gid < self.groups and self.groupwidths[gid] is not None

def checklookbehindgroup(self, gid, source):
        if self.lookbehindgroups is not None:
            if not self.checkgroup(gid):
                raise source.error('cannot refer to an open group')
            if gid >= self.lookbehindgroups:
                raise source.error('cannot refer to group defined in the same '
                                   'lookbehind subpattern')

class SubPattern:
    # a subpattern, in intermediate form
    def __init__(self, state, data=None):
        self.state = state
        if data is None:
            data = []
        self.data = data
        self.width = None

def dump(self, level=0):
        nl = True
        seqtypes = (tuple, list)
        for op, av in self.data:
            print(level*"  " + str(op), end='')
            if op is IN:
                # member sublanguage
                print()
                for op, a in av:
                    print((level+1)*"  " + str(op), a)
            elif op is BRANCH:
                print()
                for i, a in enumerate(av[1]):
                    if i:
                        print(level*"  " + "OR")
                    a.dump(level+1)
            elif op is GROUPREF_EXISTS:
                condgroup, item_yes, item_no = av
                print('', condgroup)
                item_yes.dump(level+1)
                if item_no:
                    print(level*"  " + "ELSE")
                    item_no.dump(level+1)
            elif isinstance(av, seqtypes):
                nl = False
                for a in av:
                    if isinstance(a, SubPattern):
                        if not nl:
                            print()
                        a.dump(level+1)
                        nl = True
                    else:
                        if not nl:
                            print(' ', end='')
                        print(a, end='')
                        nl = False
                if not nl:
                    print()
            else:
                print('', av)
    def __repr__(self):
        return repr(self.data)
    def __len__(self):
        return len(self.data)
    def __delitem__(self, index):
        del self.data[index]
    def __getitem__(self, index):
        if isinstance(index, slice):
            return SubPattern(self.state, self.data[index])
        return self.data[index]
    def __setitem__(self, index, code):
        self.data[index] = code
    def insert(self, index, code):
        self.data.insert(index, code)
    def append(self, code):
        self.data.append(code)
    def getwidth(self):
        # determine the width (min, max) for this subpattern
        if self.width is not None:
            return self.width
        lo = hi = 0
        for op, av in self.data:
            if op is BRANCH:
                i = MAXREPEAT - 1
                j = 0
                for av in av[1]:
                    l, h = av.getwidth()
                    i = min(i, l)
                    j = max(j, h)
                lo = lo + i
                hi = hi + j
            elif op is CALL:
                i, j = av.getwidth()
                lo = lo + i
                hi = hi + j
            elif op is SUBPATTERN:
                i, j = av[-1].getwidth()
                lo = lo + i
                hi = hi + j
            elif op in _REPEATCODES:
                i, j = av[2].getwidth()
                lo = lo + i * av[0]
                hi = hi + j * av[1]
            elif op in _UNITCODES:
                lo = lo + 1
                hi = hi + 1
            elif op is GROUPREF:
                i, j = self.state.groupwidths[av]
                lo = lo + i
                hi = hi + j
            elif op is GROUPREF_EXISTS:
                i, j = av[1].getwidth()
                if av[2] is not None:
                    l, h = av[2].getwidth()
                    i = min(i, l)
                    j = max(j, h)
                else:
                    i = 0
                lo = lo + i
                hi = hi + j
            elif op is SUCCESS:
                break
        self.width = min(lo, MAXREPEAT - 1), min(hi, MAXREPEAT)
        return self.width

class Tokenizer:
    def __init__(self, string):
        self.istext = isinstance(string, str)
        self.string = string
        if not self.istext:
            string = str(string, 'latin1')
        self.decoded_string = string
        self.index = 0
        self.next = None
        self.__next()
    def __next(self):
        index = self.index
        try:
            char = self.decoded_string[index]
        except IndexError:
            self.next = None
            return
        if char == "\\":
            index += 1
            try:
                char += self.decoded_string[index]
            except IndexError:
                raise error("bad escape (end of pattern)",
                            self.string, len(self.string) - 1) from None
        self.index = index + 1
        self.next = char
    def match(self, char):
        if char == self.next:
            self.__next()
            return True
        return False
    def get(self):
        this = self.next
        self.__next()
        return this
    def getwhile(self, n, charset):
        result = ''
        for _ in range(n):
            c = self.next
            if c not in charset:
                break
            result += c
            self.__next()
        return result
    def getuntil(self, terminator, name):
        result = ''
        while True:
            c = self.next
            self.__next()
            if c is None:
                if not result:
                    raise self.error("missing " + name)
                raise self.error("missing %s, unterminated name" % terminator,
                                 len(result))
            if c == terminator:
                if not result:
                    raise self.error("missing " + name, 1)
                break
            result += c
        return result
    @property
    def pos(self):
        return self.index - len(self.next or '')
    def tell(self):
        return self.index - len(self.next or '')
    def seek(self, index):
        self.index = index
        self.__next()

def error(self, msg, offset=0):
        return error(msg, self.string, self.tell() - offset)

def _class_escape(source, escape):
    # handle escape code inside character class
    code = ESCAPES.get(escape)
    if code:
        return code
    code = CATEGORIES.get(escape)
    if code and code[0] is IN:
        return code
    try:
        c = escape[1:2]
        if c == "x":
            # hexadecimal escape (exactly two digits)
            escape += source.getwhile(2, HEXDIGITS)
            if len(escape) != 4:
                raise source.error("incomplete escape %s" % escape, len(escape))
            return LITERAL, int(escape[2:], 16)
        elif c == "u" and source.istext:
            # unicode escape (exactly four digits)
            escape += source.getwhile(4, HEXDIGITS)
            if len(escape) != 6:
                raise source.error("incomplete escape %s" % escape, len(escape))
            return LITERAL, int(escape[2:], 16)
        elif c == "U" and source.istext:
            # unicode escape (exactly eight digits)
            escape += source.getwhile(8, HEXDIGITS)
            if len(escape) != 10:
                raise source.error("incomplete escape %s" % escape, len(escape))
            c = int(escape[2:], 16)
            chr(c) # raise ValueError for invalid code
            return LITERAL, c
        elif c == "N" and source.istext:
            import unicodedata
            # named unicode escape e.g. \N{EM DASH}
            if not source.match('{'):
                raise source.error("missing {")
            charname = source.getuntil('}', 'character name')
            try:
                c = ord(unicodedata.lookup(charname))
            except (KeyError, TypeError):
                raise source.error("undefined character name %r" % charname,
                                   len(charname) + len(r'\N{}'))
            return LITERAL, c
        elif c in OCTDIGITS:
            # octal escape (up to three digits)
            escape += source.getwhile(2, OCTDIGITS)
            c = int(escape[1:], 8)
            if c > 0o377:
                raise source.error('octal escape value %s outside of '
                                   'range 0-0o377' % escape, len(escape))
            return LITERAL, c
        elif c in DIGITS:
            raise ValueError
        if len(escape) == 2:
            if c in ASCIILETTERS:
                raise source.error('bad escape %s' % escape, len(escape))
            return LITERAL, ord(escape[1])
    except ValueError:
        pass
    raise source.error("bad escape %s" % escape, len(escape))

def _escape(source, escape, state):
    # handle escape code in expression
    code = CATEGORIES.get(escape)
    if code:
        return code
    code = ESCAPES.get(escape)
    if code:
        return code
    try:
        c = escape[1:2]
        if c == "x":
            # hexadecimal escape
            escape += source.getwhile(2, HEXDIGITS)
            if len(escape) != 4:
                raise source.error("incomplete escape %s" % escape, len(escape))
            return LITERAL, int(escape[2:], 16)
        elif c == "u" and source.istext:
            # unicode escape (exactly four digits)
            escape += source.getwhile(4, HEXDIGITS)
            if len(escape) != 6:
                raise source.error("incomplete escape %s" % escape, len(escape))
            return LITERAL, int(escape[2:], 16)
        elif c == "U" and source.istext:
            # unicode escape (exactly eight digits)
            escape += source.getwhile(8, HEXDIGITS)
            if len(escape) != 10:
                raise source.error("incomplete escape %s" % escape, len(escape))
            c = int(escape[2:], 16)
            chr(c) # raise ValueError for invalid code
            return LITERAL, c
        elif c == "N" and source.istext:
            import unicodedata
            # named unicode escape e.g. \N{EM DASH}
            if not source.match('{'):
                raise source.error("missing {")
            charname = source.getuntil('}', 'character name')
            try:
                c = ord(unicodedata.lookup(charname))
            except (KeyError, TypeError):
                raise source.error("undefined character name %r" % charname,
                                   len(charname) + len(r'\N{}'))
            return LITERAL, c
        elif c == "0":
            # octal escape
            escape += source.getwhile(2, OCTDIGITS)
            return LITERAL, int(escape[1:], 8)
        elif c in DIGITS:
            # octal escape *or* decimal group reference (sigh)
            if source.next in DIGITS:
                escape += source.get()
                if (escape[1] in OCTDIGITS and escape[2] in OCTDIGITS and
                    source.next in OCTDIGITS):
                    # got three octal digits; this is an octal escape
                    escape += source.get()
                    c = int(escape[1:], 8)
                    if c > 0o377:
                        raise source.error('octal escape value %s outside of '
                                           'range 0-0o377' % escape,
                                           len(escape))
                    return LITERAL, c
            # not an octal escape, so this is a group reference
            group = int(escape[1:])
            if group < state.groups:
                if not state.checkgroup(group):
                    raise source.error("cannot refer to an open group",
                                       len(escape))
                state.checklookbehindgroup(group, source)
                return GROUPREF, group
            raise source.error("invalid group reference %d" % group, len(escape) - 1)
        if len(escape) == 2:
            if c in ASCIILETTERS:
                raise source.error("bad escape %s" % escape, len(escape))
            return LITERAL, ord(escape[1])
    except ValueError:
        pass
    raise source.error("bad escape %s" % escape, len(escape))

def _uniq(items):
    return list(dict.fromkeys(items))

def _parse_sub(source, state, verbose, nested):
    # parse an alternation: a|b|c

items = []
    itemsappend = items.append
    sourcematch = source.match
    start = source.tell()
    while True:
        itemsappend(_parse(source, state, verbose, nested + 1,
                           not nested and not items))
        if not sourcematch("|"):
            break

if len(items) == 1:
        return items[0]

subpattern = SubPattern(state)

# check if all items share a common prefix
    while True:
        prefix = None
        for item in items:
            if not item:
                break
            if prefix is None:
                prefix = item[0]
            elif item[0] != prefix:
                break
        else:
            # all subitems start with a common "prefix".
            # move it out of the branch
            for item in items:
                del item[0]
            subpattern.append(prefix)
            continue # check next one
        break

# check if the branch can be replaced by a character set
    set = []
    for item in items:
        if len(item) != 1:
            break
        op, av = item[0]
        if op is LITERAL:
            set.append((op, av))
        elif op is IN and av[0][0] is not NEGATE:
            set.extend(av)
        else:
            break
    else:
        # we can store this as a character set instead of a
        # branch (the compiler may optimize this even more)
        subpattern.append((IN, _uniq(set)))
        return subpattern

subpattern.append((BRANCH, (None, items)))
    return subpattern

def _parse(source, state, verbose, nested, first=False):
    # parse a simple pattern
    subpattern = SubPattern(state)

# precompute constants into local variables
    subpatternappend = subpattern.append
    sourceget = source.get
    sourcematch = source.match
    _len = len
    _ord = ord

while True:

this = source.next
        if this is None:
            break # end of pattern
        if this in "|)":
            break # end of subpattern
        sourceget()

if verbose:
            # skip whitespace and comments
            if this in WHITESPACE:
                continue
            if this == "#":
                while True:
                    this = sourceget()
                    if this is None or this == "\n":
                        break
                continue

if this[0] == "\\":
            code = _escape(source, this, state)
            subpatternappend(code)

elif this not in SPECIAL_CHARS:
            subpatternappend((LITERAL, _ord(this)))

elif this == "[":
            here = source.tell() - 1
            # character set
            set = []
            setappend = set.append
##          if sourcematch(":"):
##              pass # handle character classes
            if source.next == '[':
                import warnings
                warnings.warn(
                    'Possible nested set at position %d' % source.tell(),
                    FutureWarning, stacklevel=nested + 6
                )
            negate = sourcematch("^")
            # check remaining characters
            while True:
                this = sourceget()
                if this is None:
                    raise source.error("unterminated character set",
                                       source.tell() - here)
                if this == "]" and set:
                    break
                elif this[0] == "\\":
                    code1 = _class_escape(source, this)
                else:
                    if set and this in '-&~|' and source.next == this:
                        import warnings
                        warnings.warn(
                            'Possible set %s at position %d' % (
                                'difference' if this == '-' else
                                'intersection' if this == '&' else
                                'symmetric difference' if this == '~' else
                                'union',
                                source.tell() - 1),
                            FutureWarning, stacklevel=nested + 6
                        )
                    code1 = LITERAL, _ord(this)
                if sourcematch("-"):
                    # potential range
                    that = sourceget()
                    if that is None:
                        raise source.error("unterminated character set",
                                           source.tell() - here)
                    if that == "]":
                        if code1[0] is IN:
                            code1 = code1[1][0]
                        setappend(code1)
                        setappend((LITERAL, _ord("-")))
                        break
                    if that[0] == "\\":
                        code2 = _class_escape(source, that)
                    else:
                        if that == '-':
                            import warnings
                            warnings.warn(
                                'Possible set difference at position %d' % (
                                    source.tell() - 2),
                                FutureWarning, stacklevel=nested + 6
                            )
                        code2 = LITERAL, _ord(that)
                    if code1[0] != LITERAL or code2[0] != LITERAL:
                        msg = "bad character range %s-%s" % (this, that)
                        raise source.error(msg, len(this) + 1 + len(that))
                    lo = code1[1]
                    hi = code2[1]
                    if hi < lo:
                        msg = "bad character range %s-%s" % (this, that)
                        raise source.error(msg, len(this) + 1 + len(that))
                    setappend((RANGE, (lo, hi)))
                else:
                    if code1[0] is IN:
                        code1 = code1[1][0]
                    setappend(code1)

set = _uniq(set)
            # XXX: <fl> should move set optimization to compiler!
            if _len(set) == 1 and set[0][0] is LITERAL:
                # optimization
                if negate:
                    subpatternappend((NOT_LITERAL, set[0][1]))
                else:
                    subpatternappend(set[0])
            else:
                if negate:
                    set.insert(0, (NEGATE, None))
                # charmap optimization can't be added here because
                # global flags still are not known
                subpatternappend((IN, set))

elif this in REPEAT_CHARS:
            # repeat previous item
            here = source.tell()
            if this == "?":
                min, max = 0, 1
            elif this == "*":
                min, max = 0, MAXREPEAT

elif this == "+":
                min, max = 1, MAXREPEAT
            elif this == "{":
                if source.next == "}":
                    subpatternappend((LITERAL, _ord(this)))
                    continue

min, max = 0, MAXREPEAT
                lo = hi = ""
                while source.next in DIGITS:
                    lo += sourceget()
                if sourcematch(","):
                    while source.next in DIGITS:
                        hi += sourceget()
                else:
                    hi = lo
                if not sourcematch("}"):
                    subpatternappend((LITERAL, _ord(this)))
                    source.seek(here)
                    continue

if lo:
                    min = int(lo)
                    if min >= MAXREPEAT:
                        raise OverflowError("the repetition number is too large")
                if hi:
                    max = int(hi)
                    if max >= MAXREPEAT:
                        raise OverflowError("the repetition number is too large")
                    if max < min:
                        raise source.error("min repeat greater than max repeat",
                                           source.tell() - here)
            else:
                raise AssertionError("unsupported quantifier %r" % (char,))
            # figure out which item to repeat
            if subpattern:
                item = subpattern[-1:]
            else:
                item = None
            if not item or item[0][0] is AT:
                raise source.error("nothing to repeat",
                                   source.tell() - here + len(this))
            if item[0][0] in _REPEATCODES:
                raise source.error("multiple repeat",
                                   source.tell() - here + len(this))
            if item[0][0] is SUBPATTERN:
                group, add_flags, del_flags, p = item[0][1]
                if group is None and not add_flags and not del_flags:
                    item = p
            if sourcematch("?"):
                subpattern[-1] = (MIN_REPEAT, (min, max, item))
            else:
                subpattern[-1] = (MAX_REPEAT, (min, max, item))

elif this == ".":
            subpatternappend((ANY, None))

elif this == "(":
            start = source.tell() - 1
            group = True
            name = None
            add_flags = 0
            del_flags = 0
            if sourcematch("?"):
                # options
                char = sourceget()
                if char is None:
                    raise source.error("unexpected end of pattern")
                if char == "P":
                    # python extensions
                    if sourcematch("<"):
                        # named group: skip forward to end of name
                        name = source.getuntil(">", "group name")
                        if not name.isidentifier():
                            msg = "bad character in group name %r" % name
                            raise source.error(msg, len(name) + 1)
                    elif sourcematch("="):
                        # named backreference
                        name = source.getuntil(")", "group name")
                        if not name.isidentifier():
                            msg = "bad character in group name %r" % name
                            raise source.error(msg, len(name) + 1)
                        gid = state.groupdict.get(name)
                        if gid is None:
                            msg = "unknown group name %r" % name
                            raise source.error(msg, len(name) + 1)
                        if not state.checkgroup(gid):
                            raise source.error("cannot refer to an open group",
                                               len(name) + 1)
                        state.checklookbehindgroup(gid, source)
                        subpatternappend((GROUPREF, gid))
                        continue

else:
                        char = sourceget()
                        if char is None:
                            raise source.error("unexpected end of pattern")
                        raise source.error("unknown extension ?P" + char,
                                           len(char) + 2)
                elif char == ":":
                    # non-capturing group
                    group = None
                elif char == "#":
                    # comment
                    while True:
                        if source.next is None:
                            raise source.error("missing ), unterminated comment",
                                               source.tell() - start)
                        if sourceget() == ")":
                            break
                    continue

elif char in "=!<":
                    # lookahead assertions
                    dir = 1
                    if char == "<":
                        char = sourceget()
                        if char is None:
                            raise source.error("unexpected end of pattern")
                        if char not in "=!":
                            raise source.error("unknown extension ?<" + char,
                                               len(char) + 2)
                        dir = -1 # lookbehind
                        lookbehindgroups = state.lookbehindgroups
                        if lookbehindgroups is None:
                            state.lookbehindgroups = state.groups
                    p = _parse_sub(source, state, verbose, nested + 1)
                    if dir < 0:
                        if lookbehindgroups is None:
                            state.lookbehindgroups = None
                    if not sourcematch(")"):
                        raise source.error("missing ), unterminated subpattern",
                                           source.tell() - start)
                    if char == "=":
                        subpatternappend((ASSERT, (dir, p)))
                    else:
                        subpatternappend((ASSERT_NOT, (dir, p)))
                    continue

elif char == "(":
                    # conditional backreference group
                    condname = source.getuntil(")", "group name")
                    if condname.isidentifier():
                        condgroup = state.groupdict.get(condname)
                        if condgroup is None:
                            msg = "unknown group name %r" % condname
                            raise source.error(msg, len(condname) + 1)
                    else:
                        try:
                            condgroup = int(condname)
                            if condgroup < 0:
                                raise ValueError
                        except ValueError:
                            msg = "bad character in group name %r" % condname
                            raise source.error(msg, len(condname) + 1) from None
                        if not condgroup:
                            raise source.error("bad group number",
                                               len(condname) + 1)
                        if condgroup >= MAXGROUPS:
                            msg = "invalid group reference %d" % condgroup
                            raise source.error(msg, len(condname) + 1)
                        if condgroup not in state.grouprefpos:
                            state.grouprefpos[condgroup] = (
                                source.tell() - len(condname) - 1
                            )
                    state.checklookbehindgroup(condgroup, source)
                    item_yes = _parse(source, state, verbose, nested + 1)
                    if source.match("|"):
                        item_no = _parse(source, state, verbose, nested + 1)
                        if source.next == "|":
                            raise source.error("conditional backref with more than two branches")
                    else:
                        item_no = None
                    if not source.match(")"):
                        raise source.error("missing ), unterminated subpattern",
                                           source.tell() - start)
                    subpatternappend((GROUPREF_EXISTS, (condgroup, item_yes, item_no)))
                    continue

elif char in FLAGS or char == "-":
                    # flags
                    flags = _parse_flags(source, state, char)
                    if flags is None:  # global flags
                        if not first or subpattern:
                            import warnings
                            warnings.warn(
                                'Flags not at the start of the expression %r%s'
                                ' but at position %d' % (
                                    source.string[:20],  # truncate long regexes
                                    ' (truncated)' if len(source.string) > 20 else '',
                                    start,
                                ),
                                DeprecationWarning, stacklevel=nested + 6
                            )
                        if (state.flags & SRE_FLAG_VERBOSE) and not verbose:
                            raise Verbose
                        continue

add_flags, del_flags = flags
                    group = None
                else:
                    raise source.error("unknown extension ?" + char,
                                       len(char) + 1)

# parse group contents
            if group is not None:
                try:
                    group = state.opengroup(name)
                except error as err:
                    raise source.error(err.msg, len(name) + 1) from None
            sub_verbose = ((verbose or (add_flags & SRE_FLAG_VERBOSE)) and
                           not (del_flags & SRE_FLAG_VERBOSE))
            p = _parse_sub(source, state, sub_verbose, nested + 1)
            if not source.match(")"):
                raise source.error("missing ), unterminated subpattern",
                                   source.tell() - start)
            if group is not None:
                state.closegroup(group, p)
            subpatternappend((SUBPATTERN, (group, add_flags, del_flags, p)))

elif this == "^":
            subpatternappend((AT, AT_BEGINNING))

elif this == "$":
            subpatternappend((AT, AT_END))

else:
            raise AssertionError("unsupported special character %r" % (char,))

# unpack non-capturing groups
    for i in range(len(subpattern))[::-1]:
        op, av = subpattern[i]
        if op is SUBPATTERN:
            group, add_flags, del_flags, p = av
            if group is None and not add_flags and not del_flags:
                subpattern[i: i+1] = p

return subpattern

def _parse_flags(source, state, char):
    sourceget = source.get
    add_flags = 0
    del_flags = 0
    if char != "-":
        while True:
            flag = FLAGS[char]
            if source.istext:
                if char == 'L':
                    msg = "bad inline flags: cannot use 'L' flag with a str pattern"
                    raise source.error(msg)
            else:
                if char == 'u':
                    msg = "bad inline flags: cannot use 'u' flag with a bytes pattern"
                    raise source.error(msg)
            add_flags |= flag
            if (flag & TYPE_FLAGS) and (add_flags & TYPE_FLAGS) != flag:
                msg = "bad inline flags: flags 'a', 'u' and 'L' are incompatible"
                raise source.error(msg)
            char = sourceget()
            if char is None:
                raise source.error("missing -, : or )")
            if char in ")-:":
                break
            if char not in FLAGS:
                msg = "unknown flag" if char.isalpha() else "missing -, : or )"
                raise source.error(msg, len(char))
    if char == ")":
        state.flags |= add_flags
        return None
    if add_flags & GLOBAL_FLAGS:
        raise source.error("bad inline flags: cannot turn on global flag", 1)
    if char == "-":
        char = sourceget()
        if char is None:
            raise source.error("missing flag")
        if char not in FLAGS:
            msg = "unknown flag" if char.isalpha() else "missing flag"
            raise source.error(msg, len(char))
        while True:
            flag = FLAGS[char]
            if flag & TYPE_FLAGS:
                msg = "bad inline flags: cannot turn off flags 'a', 'u' and 'L'"
                raise source.error(msg)
            del_flags |= flag
            char = sourceget()
            if char is None:
                raise source.error("missing :")
            if char == ":":
                break
            if char not in FLAGS:
                msg = "unknown flag" if char.isalpha() else "missing :"
                raise source.error(msg, len(char))
    assert char == ":"
    if del_flags & GLOBAL_FLAGS:
        raise source.error("bad inline flags: cannot turn off global flag", 1)
    if add_flags & del_flags:
        raise source.error("bad inline flags: flag turned on and off", 1)
    return add_flags, del_flags

def fix_flags(src, flags):
    # Check and fix flags according to the type of pattern (str or bytes)
    if isinstance(src, str):
        if flags & SRE_FLAG_LOCALE:
            raise ValueError("cannot use LOCALE flag with a str pattern")
        if not flags & SRE_FLAG_ASCII:
            flags |= SRE_FLAG_UNICODE
        elif flags & SRE_FLAG_UNICODE:
            raise ValueError("ASCII and UNICODE flags are incompatible")
    else:
        if flags & SRE_FLAG_UNICODE:
            raise ValueError("cannot use UNICODE flag with a bytes pattern")
        if flags & SRE_FLAG_LOCALE and flags & SRE_FLAG_ASCII:
            raise ValueError("ASCII and LOCALE flags are incompatible")
    return flags

def parse(str, flags=0, state=None):
    # parse 're' pattern into list of (opcode, argument) tuples

source = Tokenizer(str)

if state is None:
        state = State()
    state.flags = flags
    state.str = str

try:
        p = _parse_sub(source, state, flags & SRE_FLAG_VERBOSE, 0)
    except Verbose:
        # the VERBOSE flag was switched on inside the pattern.  to be
        # on the safe side, we'll parse the whole thing again...
        state = State()
        state.flags = flags | SRE_FLAG_VERBOSE
        state.str = str
        source.seek(0)
        p = _parse_sub(source, state, True, 0)

p.state.flags = fix_flags(str, p.state.flags)

if source.next is not None:
        assert source.next == ")"
        raise source.error("unbalanced parenthesis")

for g in p.state.grouprefpos:
        if g >= p.state.groups:
            msg = "invalid group reference %d" % g
            raise error(msg, str, p.state.grouprefpos[g])

if flags & SRE_FLAG_DEBUG:
        p.dump()

return p

def parse_template(source, state):
    # parse 're' replacement string into list of literals and
    # group references
    s = Tokenizer(source)
    sget = s.get
    groups = []
    literals = []
    literal = []
    lappend = literal.append
    def addgroup(index, pos):
        if index > state.groups:
            raise s.error("invalid group reference %d" % index, pos)
        if literal:
            literals.append(''.join(literal))
            del literal[:]
        groups.append((len(literals), index))
        literals.append(None)
    groupindex = state.groupindex
    while True:
        this = sget()
        if this is None:
            break # end of replacement string
        if this[0] == "\\":
            # group
            c = this[1]
            if c == "g":
                name = ""
                if not s.match("<"):
                    raise s.error("missing <")
                name = s.getuntil(">", "group name")
                if name.isidentifier():
                    try:
                        index = groupindex[name]
                    except KeyError:
                        raise IndexError("unknown group name %r" % name)
                else:
                    try:
                        index = int(name)
                        if index < 0:
                            raise ValueError
                    except ValueError:
                        raise s.error("bad character in group name %r" % name,
                                      len(name) + 1) from None
                    if index >= MAXGROUPS:
                        raise s.error("invalid group reference %d" % index,
                                      len(name) + 1)
                addgroup(index, len(name) + 1)
            elif c == "0":
                if s.next in OCTDIGITS:
                    this += sget()
                    if s.next in OCTDIGITS:
                        this += sget()
                lappend(chr(int(this[1:], 8) & 0xff))
            elif c in DIGITS:
                isoctal = False
                if s.next in DIGITS:
                    this += sget()
                    if (c in OCTDIGITS and this[2] in OCTDIGITS and
                        s.next in OCTDIGITS):
                        this += sget()
                        isoctal = True
                        c = int(this[1:], 8)
                        if c > 0o377:
                            raise s.error('octal escape value %s outside of '
                                          'range 0-0o377' % this, len(this))
                        lappend(chr(c))
                if not isoctal:
                    addgroup(int(this[1:]), len(this) - 1)
            else:
                try:
                    this = chr(ESCAPES[this][1])
                except KeyError:
                    if c in ASCIILETTERS:
                        raise s.error('bad escape %s' % this, len(this))
                lappend(this)
        else:
            lappend(this)
    if literal:
        literals.append(''.join(literal))
    if not isinstance(source, str):
        # The tokenizer implicitly decodes bytes objects as latin-1, we must
        # therefore re-encode the final representation.
        literals = [None if s is None else s.encode('latin-1') for s in literals]
    return groups, literals

def expand_template(template, match):
    g = match.group
    empty = match.string[:0]
    groups, literals = template
    literals = literals[:]
    try:
        for index, group in groups:
            literals[index] = g(group) or empty
    except IndexError:
        raise error("invalid group reference %d" % index)
    return empty.join(literals)

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