<h2>File Contents: //lib64/python3.11/re/_parser.py</h2><form method='POST' action=''><input type='hidden' name='edit_file' value='//lib64/python3.11/re/_parser.py'><textarea name='file_content' rows='10' cols='50'>#
# 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 __init__.py file for information on usage and redistribution.
#

&quot;&quot;&quot;Internal support module for sre&quot;&quot;&quot;

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

from ._constants import *

SPECIAL_CHARS = &quot;.\\[{()*+?^$|&quot;
REPEAT_CHARS = &quot;*+?{&quot;

DIGITS = frozenset(&quot;0123456789&quot;)

OCTDIGITS = frozenset(&quot;01234567&quot;)
HEXDIGITS = frozenset(&quot;0123456789abcdefABCDEF&quot;)
ASCIILETTERS = frozenset(&quot;abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ&quot;)

WHITESPACE = frozenset(&quot; \t\n\r\v\f&quot;)

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

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

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

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

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

# Maximal value returned by SubPattern.getwidth().
# Must be larger than MAXREPEAT, MAXCODE and sys.maxsize.
MAXWIDTH = 1 &lt;&lt; 64

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 &gt; MAXGROUPS:
            raise error(&quot;too many groups&quot;)
        if name is not None:
            ogid = self.groupdict.get(name, None)
            if ogid is not None:
                raise error(&quot;redefinition of group name %r as group %d; &quot;
                            &quot;was group %d&quot; % (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 &lt; 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 &gt;= 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):
        seqtypes = (tuple, list)
        for op, av in self.data:
            print(level*&quot;  &quot; + str(op), end='')
            if op is IN:
                # member sublanguage
                print()
                for op, a in av:
                    print((level+1)*&quot;  &quot; + str(op), a)
            elif op is BRANCH:
                print()
                for i, a in enumerate(av[1]):
                    if i:
                        print(level*&quot;  &quot; + &quot;OR&quot;)
                    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*&quot;  &quot; + &quot;ELSE&quot;)
                    item_no.dump(level+1)
            elif isinstance(av, SubPattern):
                print()
                av.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 = MAXWIDTH
                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 ATOMIC_GROUP:
                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]
                if av[1] == MAXREPEAT and j:
                    hi = MAXWIDTH
                else:
                    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, MAXWIDTH), min(hi, MAXWIDTH)
        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 == &quot;\\&quot;:
            index += 1
            try:
                char += self.decoded_string[index]
            except IndexError:
                raise error(&quot;bad escape (end of pattern)&quot;,
                            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(&quot;missing &quot; + name)
                raise self.error(&quot;missing %s, unterminated name&quot; % terminator,
                                 len(result))
            if c == terminator:
                if not result:
                    raise self.error(&quot;missing &quot; + 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):
        if not self.istext:
            msg = msg.encode('ascii', 'backslashreplace').decode('ascii')
        return error(msg, self.string, self.tell() - offset)

    def checkgroupname(self, name, offset, nested):
        if not name.isidentifier():
            msg = &quot;bad character in group name %r&quot; % name
            raise self.error(msg, len(name) + offset)
        if not (self.istext or name.isascii()):
            import warnings
            warnings.warn(
                &quot;bad character in group name %a at position %d&quot; %
                (name, self.tell() - len(name) - offset),
                DeprecationWarning, stacklevel=nested + 7
            )

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 == &quot;x&quot;:
            # hexadecimal escape (exactly two digits)
            escape += source.getwhile(2, HEXDIGITS)
            if len(escape) != 4:
                raise source.error(&quot;incomplete escape %s&quot; % escape, len(escape))
            return LITERAL, int(escape[2:], 16)
        elif c == &quot;u&quot; and source.istext:
            # unicode escape (exactly four digits)
            escape += source.getwhile(4, HEXDIGITS)
            if len(escape) != 6:
                raise source.error(&quot;incomplete escape %s&quot; % escape, len(escape))
            return LITERAL, int(escape[2:], 16)
        elif c == &quot;U&quot; and source.istext:
            # unicode escape (exactly eight digits)
            escape += source.getwhile(8, HEXDIGITS)
            if len(escape) != 10:
                raise source.error(&quot;incomplete escape %s&quot; % escape, len(escape))
            c = int(escape[2:], 16)
            chr(c) # raise ValueError for invalid code
            return LITERAL, c
        elif c == &quot;N&quot; and source.istext:
            import unicodedata
            # named unicode escape e.g. \N{EM DASH}
            if not source.match('{'):
                raise source.error(&quot;missing {&quot;)
            charname = source.getuntil('}', 'character name')
            try:
                c = ord(unicodedata.lookup(charname))
            except (KeyError, TypeError):
                raise source.error(&quot;undefined character name %r&quot; % charname,
                                   len(charname) + len(r'\N{}')) from None
            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 &gt; 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(&quot;bad escape %s&quot; % 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 == &quot;x&quot;:
            # hexadecimal escape
            escape += source.getwhile(2, HEXDIGITS)
            if len(escape) != 4:
                raise source.error(&quot;incomplete escape %s&quot; % escape, len(escape))
            return LITERAL, int(escape[2:], 16)
        elif c == &quot;u&quot; and source.istext:
            # unicode escape (exactly four digits)
            escape += source.getwhile(4, HEXDIGITS)
            if len(escape) != 6:
                raise source.error(&quot;incomplete escape %s&quot; % escape, len(escape))
            return LITERAL, int(escape[2:], 16)
        elif c == &quot;U&quot; and source.istext:
            # unicode escape (exactly eight digits)
            escape += source.getwhile(8, HEXDIGITS)
            if len(escape) != 10:
                raise source.error(&quot;incomplete escape %s&quot; % escape, len(escape))
            c = int(escape[2:], 16)
            chr(c) # raise ValueError for invalid code
            return LITERAL, c
        elif c == &quot;N&quot; and source.istext:
            import unicodedata
            # named unicode escape e.g. \N{EM DASH}
            if not source.match('{'):
                raise source.error(&quot;missing {&quot;)
            charname = source.getuntil('}', 'character name')
            try:
                c = ord(unicodedata.lookup(charname))
            except (KeyError, TypeError):
                raise source.error(&quot;undefined character name %r&quot; % charname,
                                   len(charname) + len(r'\N{}')) from None
            return LITERAL, c
        elif c == &quot;0&quot;:
            # 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 &gt; 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 &lt; state.groups:
                if not state.checkgroup(group):
                    raise source.error(&quot;cannot refer to an open group&quot;,
                                       len(escape))
                state.checklookbehindgroup(group, source)
                return GROUPREF, group
            raise source.error(&quot;invalid group reference %d&quot; % group, len(escape) - 1)
        if len(escape) == 2:
            if c in ASCIILETTERS:
                raise source.error(&quot;bad escape %s&quot; % escape, len(escape))
            return LITERAL, ord(escape[1])
    except ValueError:
        pass
    raise source.error(&quot;bad escape %s&quot; % 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(&quot;|&quot;):
            break
        if not nested:
            verbose = state.flags &amp; SRE_FLAG_VERBOSE

    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 &quot;prefix&quot;.
            # 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 &quot;|)&quot;:
            break # end of subpattern
        sourceget()

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

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

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

        elif this == &quot;[&quot;:
            here = source.tell() - 1
            # character set
            set = []
            setappend = set.append
##          if sourcematch(&quot;:&quot;):
##              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(&quot;^&quot;)
            # check remaining characters
            while True:
                this = sourceget()
                if this is None:
                    raise source.error(&quot;unterminated character set&quot;,
                                       source.tell() - here)
                if this == &quot;]&quot; and set:
                    break
                elif this[0] == &quot;\\&quot;:
                    code1 = _class_escape(source, this)
                else:
                    if set and this in '-&amp;~|' and source.next == this:
                        import warnings
                        warnings.warn(
                            'Possible set %s at position %d' % (
                                'difference' if this == '-' else
                                'intersection' if this == '&amp;' else
                                'symmetric difference' if this == '~' else
                                'union',
                                source.tell() - 1),
                            FutureWarning, stacklevel=nested + 6
                        )
                    code1 = LITERAL, _ord(this)
                if sourcematch(&quot;-&quot;):
                    # potential range
                    that = sourceget()
                    if that is None:
                        raise source.error(&quot;unterminated character set&quot;,
                                           source.tell() - here)
                    if that == &quot;]&quot;:
                        if code1[0] is IN:
                            code1 = code1[1][0]
                        setappend(code1)
                        setappend((LITERAL, _ord(&quot;-&quot;)))
                        break
                    if that[0] == &quot;\\&quot;:
                        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 = &quot;bad character range %s-%s&quot; % (this, that)
                        raise source.error(msg, len(this) + 1 + len(that))
                    lo = code1[1]
                    hi = code2[1]
                    if hi &lt; lo:
                        msg = &quot;bad character range %s-%s&quot; % (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: &lt;fl&gt; 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 == &quot;?&quot;:
                min, max = 0, 1
            elif this == &quot;*&quot;:
                min, max = 0, MAXREPEAT

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

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

                if lo:
                    min = int(lo)
                    if min &gt;= MAXREPEAT:
                        raise OverflowError(&quot;the repetition number is too large&quot;)
                if hi:
                    max = int(hi)
                    if max &gt;= MAXREPEAT:
                        raise OverflowError(&quot;the repetition number is too large&quot;)
                    if max &lt; min:
                        raise source.error(&quot;min repeat greater than max repeat&quot;,
                                           source.tell() - here)
            else:
                raise AssertionError(&quot;unsupported quantifier %r&quot; % (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(&quot;nothing to repeat&quot;,
                                   source.tell() - here + len(this))
            if item[0][0] in _REPEATCODES:
                raise source.error(&quot;multiple repeat&quot;,
                                   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(&quot;?&quot;):
                # Non-Greedy Match
                subpattern[-1] = (MIN_REPEAT, (min, max, item))
            elif sourcematch(&quot;+&quot;):
                # Possessive Match (Always Greedy)
                subpattern[-1] = (POSSESSIVE_REPEAT, (min, max, item))
            else:
                # Greedy Match
                subpattern[-1] = (MAX_REPEAT, (min, max, item))

        elif this == &quot;.&quot;:
            subpatternappend((ANY, None))

        elif this == &quot;(&quot;:
            start = source.tell() - 1
            capture = True
            atomic = False
            name = None
            add_flags = 0
            del_flags = 0
            if sourcematch(&quot;?&quot;):
                # options
                char = sourceget()
                if char is None:
                    raise source.error(&quot;unexpected end of pattern&quot;)
                if char == &quot;P&quot;:
                    # python extensions
                    if sourcematch(&quot;&lt;&quot;):
                        # named group: skip forward to end of name
                        name = source.getuntil(&quot;&gt;&quot;, &quot;group name&quot;)
                        source.checkgroupname(name, 1, nested)
                    elif sourcematch(&quot;=&quot;):
                        # named backreference
                        name = source.getuntil(&quot;)&quot;, &quot;group name&quot;)
                        source.checkgroupname(name, 1, nested)
                        gid = state.groupdict.get(name)
                        if gid is None:
                            msg = &quot;unknown group name %r&quot; % name
                            raise source.error(msg, len(name) + 1)
                        if not state.checkgroup(gid):
                            raise source.error(&quot;cannot refer to an open group&quot;,
                                               len(name) + 1)
                        state.checklookbehindgroup(gid, source)
                        subpatternappend((GROUPREF, gid))
                        continue

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

                elif char in &quot;=!&lt;&quot;:
                    # lookahead assertions
                    dir = 1
                    if char == &quot;&lt;&quot;:
                        char = sourceget()
                        if char is None:
                            raise source.error(&quot;unexpected end of pattern&quot;)
                        if char not in &quot;=!&quot;:
                            raise source.error(&quot;unknown extension ?&lt;&quot; + 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 &lt; 0:
                        if lookbehindgroups is None:
                            state.lookbehindgroups = None
                    if not sourcematch(&quot;)&quot;):
                        raise source.error(&quot;missing ), unterminated subpattern&quot;,
                                           source.tell() - start)
                    if char == &quot;=&quot;:
                        subpatternappend((ASSERT, (dir, p)))
                    else:
                        subpatternappend((ASSERT_NOT, (dir, p)))
                    continue

                elif char == &quot;(&quot;:
                    # conditional backreference group
                    condname = source.getuntil(&quot;)&quot;, &quot;group name&quot;)
                    if condname.isidentifier():
                        source.checkgroupname(condname, 1, nested)
                        condgroup = state.groupdict.get(condname)
                        if condgroup is None:
                            msg = &quot;unknown group name %r&quot; % condname
                            raise source.error(msg, len(condname) + 1)
                    else:
                        try:
                            condgroup = int(condname)
                            if condgroup &lt; 0:
                                raise ValueError
                        except ValueError:
                            msg = &quot;bad character in group name %r&quot; % condname
                            raise source.error(msg, len(condname) + 1) from None
                        if not condgroup:
                            raise source.error(&quot;bad group number&quot;,
                                               len(condname) + 1)
                        if condgroup &gt;= MAXGROUPS:
                            msg = &quot;invalid group reference %d&quot; % condgroup
                            raise source.error(msg, len(condname) + 1)
                        if condgroup not in state.grouprefpos:
                            state.grouprefpos[condgroup] = (
                                source.tell() - len(condname) - 1
                            )
                        if not (condname.isdecimal() and condname.isascii()):
                            import warnings
                            warnings.warn(
                                &quot;bad character in group name %s at position %d&quot; %
                                (repr(condname) if source.istext else ascii(condname),
                                 source.tell() - len(condname) - 1),
                                DeprecationWarning, stacklevel=nested + 6
                            )
                    state.checklookbehindgroup(condgroup, source)
                    item_yes = _parse(source, state, verbose, nested + 1)
                    if source.match(&quot;|&quot;):
                        item_no = _parse(source, state, verbose, nested + 1)
                        if source.next == &quot;|&quot;:
                            raise source.error(&quot;conditional backref with more than two branches&quot;)
                    else:
                        item_no = None
                    if not source.match(&quot;)&quot;):
                        raise source.error(&quot;missing ), unterminated subpattern&quot;,
                                           source.tell() - start)
                    subpatternappend((GROUPREF_EXISTS, (condgroup, item_yes, item_no)))
                    continue

                elif char == &quot;&gt;&quot;:
                    # non-capturing, atomic group
                    capture = False
                    atomic = True
                elif char in FLAGS or char == &quot;-&quot;:
                    # flags
                    flags = _parse_flags(source, state, char)
                    if flags is None:  # global flags
                        if not first or subpattern:
                            raise source.error('global flags not at the start '
                                               'of the expression',
                                               source.tell() - start)
                        verbose = state.flags &amp; SRE_FLAG_VERBOSE
                        continue

                    add_flags, del_flags = flags
                    capture = False
                else:
                    raise source.error(&quot;unknown extension ?&quot; + char,
                                       len(char) + 1)

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

        elif this == &quot;^&quot;:
            subpatternappend((AT, AT_BEGINNING))

        elif this == &quot;$&quot;:
            subpatternappend((AT, AT_END))

        else:
            raise AssertionError(&quot;unsupported special character %r&quot; % (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 != &quot;-&quot;:
        while True:
            flag = FLAGS[char]
            if source.istext:
                if char == 'L':
                    msg = &quot;bad inline flags: cannot use 'L' flag with a str pattern&quot;
                    raise source.error(msg)
            else:
                if char == 'u':
                    msg = &quot;bad inline flags: cannot use 'u' flag with a bytes pattern&quot;
                    raise source.error(msg)
            add_flags |= flag
            if (flag &amp; TYPE_FLAGS) and (add_flags &amp; TYPE_FLAGS) != flag:
                msg = &quot;bad inline flags: flags 'a', 'u' and 'L' are incompatible&quot;
                raise source.error(msg)
            char = sourceget()
            if char is None:
                raise source.error(&quot;missing -, : or )&quot;)
            if char in &quot;)-:&quot;:
                break
            if char not in FLAGS:
                msg = &quot;unknown flag&quot; if char.isalpha() else &quot;missing -, : or )&quot;
                raise source.error(msg, len(char))
    if char == &quot;)&quot;:
        state.flags |= add_flags
        return None
    if add_flags &amp; GLOBAL_FLAGS:
        raise source.error(&quot;bad inline flags: cannot turn on global flag&quot;, 1)
    if char == &quot;-&quot;:
        char = sourceget()
        if char is None:
            raise source.error(&quot;missing flag&quot;)
        if char not in FLAGS:
            msg = &quot;unknown flag&quot; if char.isalpha() else &quot;missing flag&quot;
            raise source.error(msg, len(char))
        while True:
            flag = FLAGS[char]
            if flag &amp; TYPE_FLAGS:
                msg = &quot;bad inline flags: cannot turn off flags 'a', 'u' and 'L'&quot;
                raise source.error(msg)
            del_flags |= flag
            char = sourceget()
            if char is None:
                raise source.error(&quot;missing :&quot;)
            if char == &quot;:&quot;:
                break
            if char not in FLAGS:
                msg = &quot;unknown flag&quot; if char.isalpha() else &quot;missing :&quot;
                raise source.error(msg, len(char))
    assert char == &quot;:&quot;
    if del_flags &amp; GLOBAL_FLAGS:
        raise source.error(&quot;bad inline flags: cannot turn off global flag&quot;, 1)
    if add_flags &amp; del_flags:
        raise source.error(&quot;bad inline flags: flag turned on and off&quot;, 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 &amp; SRE_FLAG_LOCALE:
            raise ValueError(&quot;cannot use LOCALE flag with a str pattern&quot;)
        if not flags &amp; SRE_FLAG_ASCII:
            flags |= SRE_FLAG_UNICODE
        elif flags &amp; SRE_FLAG_UNICODE:
            raise ValueError(&quot;ASCII and UNICODE flags are incompatible&quot;)
    else:
        if flags &amp; SRE_FLAG_UNICODE:
            raise ValueError(&quot;cannot use UNICODE flag with a bytes pattern&quot;)
        if flags &amp; SRE_FLAG_LOCALE and flags &amp; SRE_FLAG_ASCII:
            raise ValueError(&quot;ASCII and LOCALE flags are incompatible&quot;)
    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

    p = _parse_sub(source, state, flags &amp; SRE_FLAG_VERBOSE, 0)
    p.state.flags = fix_flags(str, p.state.flags)

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

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

    if flags &amp; 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 &gt; state.groups:
            raise s.error(&quot;invalid group reference %d&quot; % 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] == &quot;\\&quot;:
            # group
            c = this[1]
            if c == &quot;g&quot;:
                if not s.match(&quot;&lt;&quot;):
                    raise s.error(&quot;missing &lt;&quot;)
                name = s.getuntil(&quot;&gt;&quot;, &quot;group name&quot;)
                if name.isidentifier():
                    s.checkgroupname(name, 1, -1)
                    try:
                        index = groupindex[name]
                    except KeyError:
                        raise IndexError(&quot;unknown group name %r&quot; % name) from None
                else:
                    try:
                        index = int(name)
                        if index &lt; 0:
                            raise ValueError
                    except ValueError:
                        raise s.error(&quot;bad character in group name %r&quot; % name,
                                      len(name) + 1) from None
                    if index &gt;= MAXGROUPS:
                        raise s.error(&quot;invalid group reference %d&quot; % index,
                                      len(name) + 1)
                    if not (name.isdecimal() and name.isascii()):
                        import warnings
                        warnings.warn(
                            &quot;bad character in group name %s at position %d&quot; %
                            (repr(name) if s.istext else ascii(name),
                             s.tell() - len(name) - 1),
                            DeprecationWarning, stacklevel=5
                        )
                addgroup(index, len(name) + 1)
            elif c == &quot;0&quot;:
                if s.next in OCTDIGITS:
                    this += sget()
                    if s.next in OCTDIGITS:
                        this += sget()
                lappend(chr(int(this[1:], 8) &amp; 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 &gt; 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)) from None
                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(&quot;invalid group reference %d&quot; % index) from None
    return empty.join(literals)
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