cpython/Lib/sre_parse.py

#
# Secret Labs' Regular Expression Engine
#
# convert re-style regular expression to sre pattern
#
# Copyright (c) 1998-2000 by Secret Labs AB.  All rights reserved.
#
# Portions of this engine have been developed in cooperation with
# CNRI.  Hewlett-Packard provided funding for 2.0 integration and
# other compatibility work.
#

import string, sys

import _sre

from sre_constants import *

MAXREPEAT = 65535

# FIXME: the following might change in 2.0 final.  but for now, this
# seems to be the best way to be compatible with 1.5.2
CHARMASK = 0xff

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

DIGITS = tuple(string.digits)

OCTDIGITS = tuple("01234567")
HEXDIGITS = tuple("0123456789abcdefABCDEF")

WHITESPACE = tuple(string.whitespace)

ESCAPES = {
    r"\a": (LITERAL, 7),
    r"\b": (LITERAL, 8),
    r"\f": (LITERAL, 12),
    r"\n": (LITERAL, 10),
    r"\r": (LITERAL, 13),
    r"\t": (LITERAL, 9),
    r"\v": (LITERAL, 11),
    r"\\": (LITERAL, ord("\\"))
}

CATEGORIES = {
    r"\A": (AT, AT_BEGINNING), # 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), # 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
    "t": SRE_FLAG_TEMPLATE,
    "u": SRE_FLAG_UNICODE,
}

class State:
    def __init__(self):
        self.flags = 0
        self.groups = 1
        self.groupdict = {}
    def getgroup(self, name=None):
        gid = self.groups
        self.groups = gid + 1
        if name:
            self.groupdict[name] = gid
        return gid

class SubPattern:
    # a subpattern, in intermediate form
    def __init__(self, pattern, data=None):
        self.pattern = pattern
        if not data:
            data = []
        self.data = data
        self.width = None
    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):
        return self.data[index]
    def __setitem__(self, index, code):
        self.data[index] = code
    def __getslice__(self, start, stop):
        return SubPattern(self.pattern, self.data[start:stop])
    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:
            return self.width
        lo = hi = 0L
        for op, av in self.data:
            if op is BRANCH:
                l = sys.maxint
                h = 0
                for av in av[1]:
                    i, j = av.getwidth()
                    l = min(l, i)
                    h = min(h, j)
                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 (MIN_REPEAT, MAX_REPEAT):
                i, j = av[2].getwidth()
                lo = lo + long(i) * av[0]
                hi = hi + long(j) * av[1]
            elif op in (ANY, RANGE, IN, LITERAL, NOT_LITERAL, CATEGORY):
                lo = lo + 1
                hi = hi + 1
            elif op == SUCCESS:
                break
        self.width = int(min(lo, sys.maxint)), int(min(hi, sys.maxint))
        return self.width

class Tokenizer:
    def __init__(self, string):
        self.string = string
        self.index = 0
        self.__next()
    def __next(self):
        if self.index >= len(self.string):
            self.next = None
            return
        char = self.string[self.index]
        if char[0] == "\\":
            try:
                c = self.string[self.index + 1]
            except IndexError:
                raise error, "bogus escape"
            char = char + c
        self.index = self.index + len(char)
        self.next = char
    def match(self, char):
        if char == self.next:
            self.__next()
            return 1
        return 0
    def get(self):
        this = self.next
        self.__next()
        return this
    def tell(self):
        return self.index, self.next
    def seek(self, index):
        self.index, self.next = index

def isident(char):
    return "a" <= char <= "z" or "A" <= char <= "Z" or char == "_"

def isdigit(char):
    return "0" <= char <= "9"

def isname(name):
    # check that group name is a valid string
    if not isident(name[0]):
        return 0
    for char in name:
        if not isident(char) and not isdigit(char):
            return 0
    return 1

def _group(escape, groups):
    # check if the escape string represents a valid group
    try:
        gid = int(escape[1:])
        if gid and gid < groups:
            return gid
    except ValueError:
        pass
    return None # not a valid group

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:
        return code
    try:
        if escape[1:2] == "x":
            while source.next in HEXDIGITS:
                escape = escape + source.get()
            escape = escape[2:]
            return LITERAL, int(escape[-4:], 16) & CHARMASK
        elif str(escape[1:2]) in OCTDIGITS:
            while source.next in OCTDIGITS:
                escape = escape + source.get()
            escape = escape[1:]
            return LITERAL, int(escape[-6:], 8) & CHARMASK
        if len(escape) == 2:
            return LITERAL, ord(escape[1])
    except ValueError:
        pass
    raise error, "bogus escape: %s" % repr(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:
        if escape[1:2] == "x":
            while source.next in HEXDIGITS:
                escape = escape + source.get()
            escape = escape[2:]
            return LITERAL, int(escape[-4:], 16) & CHARMASK
        elif escape[1:2] in DIGITS:
            while 1:
                group = _group(escape, state.groups)
                if group:
                    if (not source.next or
                        not _group(escape + source.next, state.groups)):
                        return GROUP, group
                    escape = escape + source.get()
                elif source.next in OCTDIGITS:
                    escape = escape + source.get()
                else:
                    break
            escape = escape[1:]
            return LITERAL, int(escape[-6:], 8) & CHARMASK
        if len(escape) == 2:
            return LITERAL, ord(escape[1])
    except ValueError:
        pass
    raise error, "bogus escape: %s" % repr(escape)

def _branch(pattern, items):
    # form a branch operator from a set of items

    subpattern = SubPattern(pattern)

    # check if all items share a common prefix
    while 1:
        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
    for item in items:
        if len(item) != 1 or item[0][0] != LITERAL:
            break
    else:
        # we can store this as a character set instead of a
        # branch (FIXME: use a range if possible)
        set = []
        for item in items:
            set.append(item[0])
        subpattern.append((IN, set))
        return subpattern

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

def _parse(source, state):

    # parse regular expression pattern into an operator list.

    subpattern = SubPattern(state)

    while 1:

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

        if state.flags & SRE_FLAG_VERBOSE:
            # skip whitespace and comments
            if this in WHITESPACE:
                continue
            if this == "#":
                while 1:
                    this = source.get()
                    if this in (None, "\n"):
                        break
                continue

        if this and this[0] not in SPECIAL_CHARS:
            subpattern.append((LITERAL, ord(this)))

        elif this == "[":
            # character set
            set = []
##          if source.match(":"):
##              pass # handle character classes
            if source.match("^"):
                set.append((NEGATE, None))
            # check remaining characters
            start = set[:]
            while 1:
                this = source.get()
                if this == "]" and set != start:
                    break
                elif this and this[0] == "\\":
                    code1 = _class_escape(source, this)
                elif this:
                    code1 = LITERAL, ord(this)
                else:
                    raise error, "unexpected end of regular expression"
                if source.match("-"):
                    # potential range
                    this = source.get()
                    if this == "]":
                        set.append(code1)
                        set.append((LITERAL, ord("-")))
                        break
                    else:
                        if this[0] == "\\":
                            code2 = _class_escape(source, this)
                        else:
                            code2 = LITERAL, ord(this)
                        if code1[0] != LITERAL or code2[0] != LITERAL:
                            raise error, "illegal range"
                        set.append((RANGE, (code1[1], code2[1])))
                else:
                    if code1[0] is IN:
                        code1 = code1[1][0]
                    set.append(code1)

            # FIXME: <fl> move set optimization to compiler!
            if len(set)==1 and set[0][0] is LITERAL:
                subpattern.append(set[0]) # optimization
            elif len(set)==2 and set[0][0] is NEGATE and set[1][0] is LITERAL:
                subpattern.append((NOT_LITERAL, set[1][1])) # optimization
            else:
                # FIXME: <fl> add charmap optimization
                subpattern.append((IN, set))

        elif this and this[0] in REPEAT_CHARS:
            # repeat previous item
            if this == "?":
                min, max = 0, 1
            elif this == "*":
                min, max = 0, MAXREPEAT
            elif this == "+":
                min, max = 1, MAXREPEAT
            elif this == "{":
                here = source.tell()
                min, max = 0, MAXREPEAT
                lo = hi = ""
                while source.next in DIGITS:
                    lo = lo + source.get()
                if source.match(","):
                    while source.next in DIGITS:
                        hi = hi + source.get()
                else:
                    hi = lo
                if not source.match("}"):
                    subpattern.append((LITERAL, ord(this)))
                    source.seek(here)
                    continue
                if lo:
                    min = int(lo)
                if hi:
                    max = int(hi)
                # FIXME: <fl> check that hi >= lo!
            else:
                raise error, "not supported"
            # figure out which item to repeat
            if subpattern:
                item = subpattern[-1:]
            else:
                raise error, "nothing to repeat"
            if source.match("?"):
                subpattern[-1] = (MIN_REPEAT, (min, max, item))
            else:
                subpattern[-1] = (MAX_REPEAT, (min, max, item))

        elif this == ".":
            subpattern.append((ANY, None))

        elif this == "(":
            group = 1
            name = None
            if source.match("?"):
                group = 0
                # options
                if source.match("P"):
                    # python extensions
                    if source.match("<"):
                        # named group: skip forward to end of name
                        name = ""
                        while 1:
                            char = source.get()
                            if char is None:
                                raise error, "unterminated name"
                            if char == ">":
                                break
                            name = name + char
                        group = 1
                        if not isname(name):
                            raise error, "illegal character in group name"
                    elif source.match("="):
                        # named backreference
                        name = ""
                        while 1:
                            char = source.get()
                            if char is None:
                                raise error, "unterminated name"
                            if char == ")":
                                break
                            name = name + char
                        if not isname(name):
                            raise error, "illegal character in group name"
                        gid = state.groupdict.get(name)
                        if gid is None:
                            raise error, "unknown group name"
                        subpattern.append((GROUP, gid))
                    elif source.match("#"):
                        index = ""
                        while 1:
                            char = source.get()
                            if char is None:
                                raise error, "unterminated index"
                            if char == ")":
                                break
                            index = index + char
                        try:
                            index = int(index)
                            if index < 0 or index > MAXREPEAT:
                                raise ValueError
                        except ValueError:
                            raise error, "illegal index"
                        subpattern.append((INDEX, index))
                        continue
                    else:
                        char = source.get()
                        if char is None:
                            raise error, "unexpected end of pattern"
                        raise error, "unknown specifier: ?P%s" % char
                elif source.match(":"):
                    # non-capturing group
                    group = 2
                elif source.match("#"):
                    # comment
                    while 1:
                        if source.next is None or source.next == ")":
                            break
                        source.get()
                elif source.next in ("=", "!"):
                    # lookahead assertions
                    char = source.get()
                    b = []
                    while 1:
                        p = _parse(source, state)
                        if source.next == ")":
                            if b:
                                b.append(p)
                                p = _branch(state, b)
                            if char == "=":
                                subpattern.append((ASSERT, p))
                            else:
                                subpattern.append((ASSERT_NOT, p))
                            break
                        elif source.match("|"):
                            b.append(p)
                        else:
                            raise error, "pattern not properly closed"
                else:
                    # flags
                    while FLAGS.has_key(source.next):
                        state.flags = state.flags | FLAGS[source.get()]
            if group:
                # parse group contents
                b = []
                if group == 2:
                    # anonymous group
                    group = None
                else:
                    group = state.getgroup(name)
                while 1:
                    p = _parse(source, state)
                    if group is not None:
                        p.append((INDEX, group))
                    if source.match(")"):
                        if b:
                            b.append(p)
                            p = _branch(state, b)
                        subpattern.append((SUBPATTERN, (group, p)))
                        break
                    elif source.match("|"):
                        b.append(p)
                    else:
                        raise error, "group not properly closed"
            else:
                while 1:
                    char = source.get()
                    if char is None or char == ")":
                        break
                    raise error, "unknown extension"

        elif this == "^":
            subpattern.append((AT, AT_BEGINNING))

        elif this == "$":
            subpattern.append((AT, AT_END))

        elif this and this[0] == "\\":
            code = _escape(source, this, state)
            subpattern.append(code)

        else:
            raise error, "parser error"

    return subpattern

def parse(pattern, flags=0):
    # parse 're' pattern into list of (opcode, argument) tuples
    source = Tokenizer(pattern)
    state = State()
    state.flags = flags
    b = []
    while 1:
        p = _parse(source, state)
        tail = source.get()
        if tail == "|":
            b.append(p)
        elif tail == ")":
            raise error, "unbalanced parenthesis"
        elif tail is None:
            if b:
                b.append(p)
                p = _branch(state, b)
            break
        else:
            raise error, "bogus characters at end of regular expression"
    return p

def parse_template(source, pattern):
    # parse 're' replacement string into list of literals and
    # group references
    s = Tokenizer(source)
    p = []
    a = p.append
    while 1:
        this = s.get()
        if this is None:
            break # end of replacement string
        if this and this[0] == "\\":
            # group
            if this == "\\g":
                name = ""
                if s.match("<"):
                    while 1:
                        char = s.get()
                        if char is None:
                            raise error, "unterminated group name"
                        if char == ">":
                            break
                        name = name + char
                if not name:
                    raise error, "bad group name"
                try:
                    index = int(name)
                except ValueError:
                    if not isname(name):
                        raise error, "illegal character in group name"
                    try:
                        index = pattern.groupindex[name]
                    except KeyError:
                        raise IndexError, "unknown group name"
                a((MARK, index))
            elif len(this) > 1 and this[1] in DIGITS:
                code = None
                while 1:
                    group = _group(this, pattern.groups+1)
                    if group:
                        if (not s.next or
                            not _group(this + s.next, pattern.groups+1)):
                            code = MARK, int(group)
                            break
                    elif s.next in OCTDIGITS:
                        this = this + s.get()
                    else:
                        break
                if not code:
                    this = this[1:]
                    code = LITERAL, int(this[-6:], 8) & CHARMASK
                a(code)
            else:
                try:
                    a(ESCAPES[this])
                except KeyError:
                    for c in this:
                        a((LITERAL, ord(c)))
        else:
            a((LITERAL, ord(this)))
    return p

def expand_template(template, match):
    # FIXME: <fl> this is sooooo slow.  drop in the slicelist
    # code instead
    p = []
    a = p.append
    sep = match.string[:0]
    if type(sep) is type(""):
        char = chr
    else:
        char = unichr
    for c, s in template:
        if c is LITERAL:
            a(char(s))
        elif c is MARK:
            s = match.group(s)
            if s is None:
                raise error, "empty group"
            a(s)
    return sep.join(p)