Lib/sre_parse.py

   1 #
   2 # Secret Labs' Regular Expression Engine
   3 #
   4 # convert re-style regular expression to sre pattern
   5 #
   6 # Copyright (c) 1998-2001 by Secret Labs AB.  All rights reserved.
   7 #
   8 # See the sre.py file for information on usage and redistribution.
   9 #
  10
  11 """Internal support module for sre"""
  12
  13 # XXX: show string offset and offending character for all errors
  14
  15 import sys
  16
  17 from sre_constants import *
  18
  19 def set(seq):
  20     s = {}
  21     for elem in seq:
  22         s[elem] = 1
  23     return s
  24
  25 SPECIAL_CHARS = ".\\[{()*+?^$|"
  26 REPEAT_CHARS = "*+?{"
  27
  28 DIGITS = set("0123456789")
  29
  30 OCTDIGITS = set("01234567")
  31 HEXDIGITS = set("0123456789abcdefABCDEF")
  32
  33 WHITESPACE = set(" \t\n\r\v\f")
  34
  35 ESCAPES = {
  36     r"\a": (LITERAL, ord("\a")),
  37     r"\b": (LITERAL, ord("\b")),
  38     r"\f": (LITERAL, ord("\f")),
  39     r"\n": (LITERAL, ord("\n")),
  40     r"\r": (LITERAL, ord("\r")),
  41     r"\t": (LITERAL, ord("\t")),
  42     r"\v": (LITERAL, ord("\v")),
  43     r"\\": (LITERAL, ord("\\"))
  44 }
  45
  46 CATEGORIES = {
  47     r"\A": (AT, AT_BEGINNING_STRING), # start of string
  48     r"\b": (AT, AT_BOUNDARY),
  49     r"\B": (AT, AT_NON_BOUNDARY),
  50     r"\d": (IN, [(CATEGORY, CATEGORY_DIGIT)]),
  51     r"\D": (IN, [(CATEGORY, CATEGORY_NOT_DIGIT)]),
  52     r"\s": (IN, [(CATEGORY, CATEGORY_SPACE)]),
  53     r"\S": (IN, [(CATEGORY, CATEGORY_NOT_SPACE)]),
  54     r"\w": (IN, [(CATEGORY, CATEGORY_WORD)]),
  55     r"\W": (IN, [(CATEGORY, CATEGORY_NOT_WORD)]),
  56     r"\Z": (AT, AT_END_STRING), # end of string
  57 }
  58
  59 FLAGS = {
  60     # standard flags
  61     "i": SRE_FLAG_IGNORECASE,
  62     "L": SRE_FLAG_LOCALE,
  63     "m": SRE_FLAG_MULTILINE,
  64     "s": SRE_FLAG_DOTALL,
  65     "x": SRE_FLAG_VERBOSE,
  66     # extensions
  67     "t": SRE_FLAG_TEMPLATE,
  68     "u": SRE_FLAG_UNICODE,
  69 }
  70
  71 class Pattern:
  72     # master pattern object.  keeps track of global attributes
  73     def __init__(self):
  74         self.flags = 0
  75         self.open = []
  76         self.groups = 1
  77         self.groupdict = {}
  78     def opengroup(self, name=None):
  79         gid = self.groups
  80         self.groups = gid + 1
  81         if name is not None:
  82             ogid = self.groupdict.get(name, None)
  83             if ogid is not None:
  84                 raise error, ("redefinition of group name %s as group %d; "
  85                               "was group %d" % (repr(name), gid,  ogid))
  86             self.groupdict[name] = gid
  87         self.open.append(gid)
  88         return gid
  89     def closegroup(self, gid):
  90         self.open.remove(gid)
  91     def checkgroup(self, gid):
  92         return gid < self.groups and gid not in self.open
  93
  94 class SubPattern:
  95     # a subpattern, in intermediate form
  96     def __init__(self, pattern, data=None):
  97         self.pattern = pattern
  98         if data is None:
  99             data = []
 100         self.data = data
 101         self.width = None
 102     def dump(self, level=0):
 103         nl = 1
 104         seqtypes = type(()), type([])
 105         for op, av in self.data:
 106             print level*"  " + op,; nl = 0
 107             if op == "in":
 108                 # member sublanguage
 109                 print; nl = 1
 110                 for op, a in av:
 111                     print (level+1)*"  " + op, a
 112             elif op == "branch":
 113                 print; nl = 1
 114                 i = 0
 115                 for a in av[1]:
 116                     if i > 0:
 117                         print level*"  " + "or"
 118                     a.dump(level+1); nl = 1
 119                     i = i + 1
 120             elif type(av) in seqtypes:
 121                 for a in av:
 122                     if isinstance(a, SubPattern):
 123                         if not nl: print
 124                         a.dump(level+1); nl = 1
 125                     else:
 126                         print a, ; nl = 0
 127             else:
 128                 print av, ; nl = 0
 129             if not nl: print
 130     def __repr__(self):
 131         return repr(self.data)
 132     def __len__(self):
 133         return len(self.data)
 134     def __delitem__(self, index):
 135         del self.data[index]
 136     def __getitem__(self, index):
 137         return self.data[index]
 138     def __setitem__(self, index, code):
 139         self.data[index] = code
 140     def __getslice__(self, start, stop):
 141         return SubPattern(self.pattern, self.data[start:stop])
 142     def insert(self, index, code):
 143         self.data.insert(index, code)
 144     def append(self, code):
 145         self.data.append(code)
 146     def getwidth(self):
 147         # determine the width (min, max) for this subpattern
 148         if self.width:
 149             return self.width
 150         lo = hi = 0L
 151         UNITCODES = (ANY, RANGE, IN, LITERAL, NOT_LITERAL, CATEGORY)
 152         REPEATCODES = (MIN_REPEAT, MAX_REPEAT)
 153         for op, av in self.data:
 154             if op is BRANCH:
 155                 i = sys.maxint
 156                 j = 0
 157                 for av in av[1]:
 158                     l, h = av.getwidth()
 159                     i = min(i, l)
 160                     j = max(j, h)
 161                 lo = lo + i
 162                 hi = hi + j
 163             elif op is CALL:
 164                 i, j = av.getwidth()
 165                 lo = lo + i
 166                 hi = hi + j
 167             elif op is SUBPATTERN:
 168                 i, j = av[1].getwidth()
 169                 lo = lo + i
 170                 hi = hi + j
 171             elif op in REPEATCODES:
 172                 i, j = av[2].getwidth()
 173                 lo = lo + long(i) * av[0]
 174                 hi = hi + long(j) * av[1]
 175             elif op in UNITCODES:
 176                 lo = lo + 1
 177                 hi = hi + 1
 178             elif op == SUCCESS:
 179                 break
 180         self.width = int(min(lo, sys.maxint)), int(min(hi, sys.maxint))
 181         return self.width
 182
 183 class Tokenizer:
 184     def __init__(self, string):
 185         self.string = string
 186         self.index = 0
 187         self.__next()
 188     def __next(self):
 189         if self.index >= len(self.string):
 190             self.next = None
 191             return
 192         char = self.string[self.index]
 193         if char[0] == "\\":
 194             try:
 195                 c = self.string[self.index + 1]
 196             except IndexError:
 197                 raise error, "bogus escape (end of line)"
 198             char = char + c
 199         self.index = self.index + len(char)
 200         self.next = char
 201     def match(self, char, skip=1):
 202         if char == self.next:
 203             if skip:
 204                 self.__next()
 205             return 1
 206         return 0
 207     def get(self):
 208         this = self.next
 209         self.__next()
 210         return this
 211     def tell(self):
 212         return self.index, self.next
 213     def seek(self, index):
 214         self.index, self.next = index
 215
 216 def isident(char):
 217     return "a" <= char <= "z" or "A" <= char <= "Z" or char == "_"
 218
 219 def isdigit(char):
 220     return "0" <= char <= "9"
 221
 222 def isname(name):
 223     # check that group name is a valid string
 224     if not isident(name[0]):
 225         return False
 226     for char in name[1:]:
 227         if not isident(char) and not isdigit(char):
 228             return False
 229     return True
 230
 231 def _class_escape(source, escape):
 232     # handle escape code inside character class
 233     code = ESCAPES.get(escape)
 234     if code:
 235         return code
 236     code = CATEGORIES.get(escape)
 237     if code:
 238         return code
 239     try:
 240         c = escape[1:2]
 241         if c == "x":
 242             # hexadecimal escape (exactly two digits)
 243             while source.next in HEXDIGITS and len(escape) < 4:
 244                 escape = escape + source.get()
 245             escape = escape[2:]
 246             if len(escape) != 2:
 247                 raise error, "bogus escape: %s" % repr("\\" + escape)
 248             return LITERAL, int(escape, 16) & 0xff
 249         elif c in OCTDIGITS:
 250             # octal escape (up to three digits)
 251             while source.next in OCTDIGITS and len(escape) < 4:
 252                 escape = escape + source.get()
 253             escape = escape[1:]
 254             return LITERAL, int(escape, 8) & 0xff
 255         elif c in DIGITS:
 256             raise error, "bogus escape: %s" % repr(escape)
 257         if len(escape) == 2:
 258             return LITERAL, ord(escape[1])
 259     except ValueError:
 260         pass
 261     raise error, "bogus escape: %s" % repr(escape)
 262
 263 def _escape(source, escape, state):
 264     # handle escape code in expression
 265     code = CATEGORIES.get(escape)
 266     if code:
 267         return code
 268     code = ESCAPES.get(escape)
 269     if code:
 270         return code
 271     try:
 272         c = escape[1:2]
 273         if c == "x":
 274             # hexadecimal escape
 275             while source.next in HEXDIGITS and len(escape) < 4:
 276                 escape = escape + source.get()
 277             if len(escape) != 4:
 278                 raise ValueError
 279             return LITERAL, int(escape[2:], 16) & 0xff
 280         elif c == "0":
 281             # octal escape
 282             while source.next in OCTDIGITS and len(escape) < 4:
 283                 escape = escape + source.get()
 284             return LITERAL, int(escape[1:], 8) & 0xff
 285         elif c in DIGITS:
 286             # octal escape *or* decimal group reference (sigh)
 287             if source.next in DIGITS:
 288                 escape = escape + source.get()
 289                 if (escape[1] in OCTDIGITS and escape[2] in OCTDIGITS and
 290                     source.next in OCTDIGITS):
 291                     # got three octal digits; this is an octal escape
 292                     escape = escape + source.get()
 293                     return LITERAL, int(escape[1:], 8) & 0xff
 294             # not an octal escape, so this is a group reference
 295             group = int(escape[1:])
 296             if group < state.groups:
 297                 if not state.checkgroup(group):
 298                     raise error, "cannot refer to open group"
 299                 return GROUPREF, group
 300             raise ValueError
 301         if len(escape) == 2:
 302             return LITERAL, ord(escape[1])
 303     except ValueError:
 304         pass
 305     raise error, "bogus escape: %s" % repr(escape)
 306
 307 def _parse_sub(source, state, nested=1):
 308     # parse an alternation: a|b|c
 309
 310     items = []
 311     itemsappend = items.append
 312     sourcematch = source.match
 313     while 1:
 314         itemsappend(_parse(source, state))
 315         if sourcematch("|"):
 316             continue
 317         if not nested:
 318             break
 319         if not source.next or sourcematch(")", 0):
 320             break
 321         else:
 322             raise error, "pattern not properly closed"
 323
 324     if len(items) == 1:
 325         return items[0]
 326
 327     subpattern = SubPattern(state)
 328     subpatternappend = subpattern.append
 329
 330     # check if all items share a common prefix
 331     while 1:
 332         prefix = None
 333         for item in items:
 334             if not item:
 335                 break
 336             if prefix is None:
 337                 prefix = item[0]
 338             elif item[0] != prefix:
 339                 break
 340         else:
 341             # all subitems start with a common "prefix".
 342             # move it out of the branch
 343             for item in items:
 344                 del item[0]
 345             subpatternappend(prefix)
 346             continue # check next one
 347         break
 348
 349     # check if the branch can be replaced by a character set
 350     for item in items:
 351         if len(item) != 1 or item[0][0] != LITERAL:
 352             break
 353     else:
 354         # we can store this as a character set instead of a
 355         # branch (the compiler may optimize this even more)
 356         set = []
 357         setappend = set.append
 358         for item in items:
 359             setappend(item[0])
 360         subpatternappend((IN, set))
 361         return subpattern
 362
 363     subpattern.append((BRANCH, (None, items)))
 364     return subpattern
 365
 366 def _parse_sub_cond(source, state, condgroup):
 367     item_yes = _parse(source, state)
 368     if source.match("|"):
 369         item_no = _parse(source, state)
 370         if source.match("|"):
 371             raise error, "conditional backref with more than two branches"
 372     else:
 373         item_no = None
 374     if source.next and not source.match(")", 0):
 375         raise error, "pattern not properly closed"
 376     subpattern = SubPattern(state)
 377     subpattern.append((GROUPREF_EXISTS, (condgroup, item_yes, item_no)))
 378     return subpattern
 379
 380 _PATTERNENDERS = set("|)")
 381 _ASSERTCHARS = set("=!<")
 382 _LOOKBEHINDASSERTCHARS = set("=!")
 383 _REPEATCODES = set([MIN_REPEAT, MAX_REPEAT])
 384
 385 def _parse(source, state):
 386     # parse a simple pattern
 387     subpattern = SubPattern(state)
 388
 389     # precompute constants into local variables
 390     subpatternappend = subpattern.append
 391     sourceget = source.get
 392     sourcematch = source.match
 393     _len = len
 394     PATTERNENDERS = _PATTERNENDERS
 395     ASSERTCHARS = _ASSERTCHARS
 396     LOOKBEHINDASSERTCHARS = _LOOKBEHINDASSERTCHARS
 397     REPEATCODES = _REPEATCODES
 398
 399     while 1:
 400
 401         if source.next in PATTERNENDERS:
 402             break # end of subpattern
 403         this = sourceget()
 404         if this is None:
 405             break # end of pattern
 406
 407         if state.flags & SRE_FLAG_VERBOSE:
 408             # skip whitespace and comments
 409             if this in WHITESPACE:
 410                 continue
 411             if this == "#":
 412                 while 1:
 413                     this = sourceget()
 414                     if this in (None, "\n"):
 415                         break
 416                 continue
 417
 418         if this and this[0] not in SPECIAL_CHARS:
 419             subpatternappend((LITERAL, ord(this)))
 420
 421         elif this == "[":
 422             # character set
 423             set = []
 424             setappend = set.append
 425 ##          if sourcematch(":"):
 426 ##              pass # handle character classes
 427             if sourcematch("^"):
 428                 setappend((NEGATE, None))
 429             # check remaining characters
 430             start = set[:]
 431             while 1:
 432                 this = sourceget()
 433                 if this == "]" and set != start:
 434                     break
 435                 elif this and this[0] == "\\":
 436                     code1 = _class_escape(source, this)
 437                 elif this:
 438                     code1 = LITERAL, ord(this)
 439                 else:
 440                     raise error, "unexpected end of regular expression"
 441                 if sourcematch("-"):
 442                     # potential range
 443                     this = sourceget()
 444                     if this == "]":
 445                         if code1[0] is IN:
 446                             code1 = code1[1][0]
 447                         setappend(code1)
 448                         setappend((LITERAL, ord("-")))
 449                         break
 450                     elif this:
 451                         if this[0] == "\\":
 452                             code2 = _class_escape(source, this)
 453                         else:
 454                             code2 = LITERAL, ord(this)
 455                         if code1[0] != LITERAL or code2[0] != LITERAL:
 456                             raise error, "bad character range"
 457                         lo = code1[1]
 458                         hi = code2[1]
 459                         if hi < lo:
 460                             raise error, "bad character range"
 461                         setappend((RANGE, (lo, hi)))
 462                     else:
 463                         raise error, "unexpected end of regular expression"
 464                 else:
 465                     if code1[0] is IN:
 466                         code1 = code1[1][0]
 467                     setappend(code1)
 468
 469             # XXX: <fl> should move set optimization to compiler!
 470             if _len(set)==1 and set[0][0] is LITERAL:
 471                 subpatternappend(set[0]) # optimization
 472             elif _len(set)==2 and set[0][0] is NEGATE and set[1][0] is LITERAL:
 473                 subpatternappend((NOT_LITERAL, set[1][1])) # optimization
 474             else:
 475                 # XXX: <fl> should add charmap optimization here
 476                 subpatternappend((IN, set))
 477
 478         elif this and this[0] in REPEAT_CHARS:
 479             # repeat previous item
 480             if this == "?":
 481                 min, max = 0, 1
 482             elif this == "*":
 483                 min, max = 0, MAXREPEAT
 484
 485             elif this == "+":
 486                 min, max = 1, MAXREPEAT
 487             elif this == "{":
 488                 if source.next == "}":
 489                     subpatternappend((LITERAL, ord(this)))
 490                     continue
 491                 here = source.tell()
 492                 min, max = 0, MAXREPEAT
 493                 lo = hi = ""
 494                 while source.next in DIGITS:
 495                     lo = lo + source.get()
 496                 if sourcematch(","):
 497                     while source.next in DIGITS:
 498                         hi = hi + sourceget()
 499                 else:
 500                     hi = lo
 501                 if not sourcematch("}"):
 502                     subpatternappend((LITERAL, ord(this)))
 503                     source.seek(here)
 504                     continue
 505                 if lo:
 506                     min = int(lo)
 507                 if hi:
 508                     max = int(hi)
 509                 if max < min:
 510                     raise error, "bad repeat interval"
 511             else:
 512                 raise error, "not supported"
 513             # figure out which item to repeat
 514             if subpattern:
 515                 item = subpattern[-1:]
 516             else:
 517                 item = None
 518             if not item or (_len(item) == 1 and item[0][0] == AT):
 519                 raise error, "nothing to repeat"
 520             if item[0][0] in REPEATCODES:
 521                 raise error, "multiple repeat"
 522             if sourcematch("?"):
 523                 subpattern[-1] = (MIN_REPEAT, (min, max, item))
 524             else:
 525                 subpattern[-1] = (MAX_REPEAT, (min, max, item))
 526
 527         elif this == ".":
 528             subpatternappend((ANY, None))
 529
 530         elif this == "(":
 531             group = 1
 532             name = None
 533             condgroup = None
 534             if sourcematch("?"):
 535                 group = 0
 536                 # options
 537                 if sourcematch("P"):
 538                     # python extensions
 539                     if sourcematch("<"):
 540                         # named group: skip forward to end of name
 541                         name = ""
 542                         while 1:
 543                             char = sourceget()
 544                             if char is None:
 545                                 raise error, "unterminated name"
 546                             if char == ">":
 547                                 break
 548                             name = name + char
 549                         group = 1
 550                         if not isname(name):
 551                             raise error, "bad character in group name"
 552                     elif sourcematch("="):
 553                         # named backreference
 554                         name = ""
 555                         while 1:
 556                             char = sourceget()
 557                             if char is None:
 558                                 raise error, "unterminated name"
 559                             if char == ")":
 560                                 break
 561                             name = name + char
 562                         if not isname(name):
 563                             raise error, "bad character in group name"
 564                         gid = state.groupdict.get(name)
 565                         if gid is None:
 566                             raise error, "unknown group name"
 567                         subpatternappend((GROUPREF, gid))
 568                         continue
 569                     else:
 570                         char = sourceget()
 571                         if char is None:
 572                             raise error, "unexpected end of pattern"
 573                         raise error, "unknown specifier: ?P%s" % char
 574                 elif sourcematch(":"):
 575                     # non-capturing group
 576                     group = 2
 577                 elif sourcematch("#"):
 578                     # comment
 579                     while 1:
 580                         if source.next is None or source.next == ")":
 581                             break
 582                         sourceget()
 583                     if not sourcematch(")"):
 584                         raise error, "unbalanced parenthesis"
 585                     continue
 586                 elif source.next in ASSERTCHARS:
 587                     # lookahead assertions
 588                     char = sourceget()
 589                     dir = 1
 590                     if char == "<":
 591                         if source.next not in LOOKBEHINDASSERTCHARS:
 592                             raise error, "syntax error"
 593                         dir = -1 # lookbehind
 594                         char = sourceget()
 595                     p = _parse_sub(source, state)
 596                     if not sourcematch(")"):
 597                         raise error, "unbalanced parenthesis"
 598                     if char == "=":
 599                         subpatternappend((ASSERT, (dir, p)))
 600                     else:
 601                         subpatternappend((ASSERT_NOT, (dir, p)))
 602                     continue
 603                 elif sourcematch("("):
 604                     # conditional backreference group
 605                     condname = ""
 606                     while 1:
 607                         char = sourceget()
 608                         if char is None:
 609                             raise error, "unterminated name"
 610                         if char == ")":
 611                             break
 612                         condname = condname + char
 613                     group = 2
 614                     if isname(condname):
 615                         condgroup = state.groupdict.get(condname)
 616                         if condgroup is None:
 617                             raise error, "unknown group name"
 618                     else:
 619                         try:
 620                             condgroup = int(condname)
 621                         except ValueError:
 622                             raise error, "bad character in group name"
 623                 else:
 624                     # flags
 625                     if not source.next in FLAGS:
 626                         raise error, "unexpected end of pattern"
 627                     while source.next in FLAGS:
 628                         state.flags = state.flags | FLAGS[sourceget()]
 629             if group:
 630                 # parse group contents
 631                 if group == 2:
 632                     # anonymous group
 633                     group = None
 634                 else:
 635                     group = state.opengroup(name)
 636                 if condgroup:
 637                     p = _parse_sub_cond(source, state, condgroup)
 638                 else:
 639                     p = _parse_sub(source, state)
 640                 if not sourcematch(")"):
 641                     raise error, "unbalanced parenthesis"
 642                 if group is not None:
 643                     state.closegroup(group)
 644                 subpatternappend((SUBPATTERN, (group, p)))
 645             else:
 646                 while 1:
 647                     char = sourceget()
 648                     if char is None:
 649                         raise error, "unexpected end of pattern"
 650                     if char == ")":
 651                         break
 652                     raise error, "unknown extension"
 653
 654         elif this == "^":
 655             subpatternappend((AT, AT_BEGINNING))
 656
 657         elif this == "$":
 658             subpattern.append((AT, AT_END))
 659
 660         elif this and this[0] == "\\":
 661             code = _escape(source, this, state)
 662             subpatternappend(code)
 663
 664         else:
 665             raise error, "parser error"
 666
 667     return subpattern
 668
 669 def parse(str, flags=0, pattern=None):
 670     # parse 're' pattern into list of (opcode, argument) tuples
 671
 672     source = Tokenizer(str)
 673
 674     if pattern is None:
 675         pattern = Pattern()
 676     pattern.flags = flags
 677     pattern.str = str
 678
 679     p = _parse_sub(source, pattern, 0)
 680
 681     tail = source.get()
 682     if tail == ")":
 683         raise error, "unbalanced parenthesis"
 684     elif tail:
 685         raise error, "bogus characters at end of regular expression"
 686
 687     if flags & SRE_FLAG_DEBUG:
 688         p.dump()
 689
 690     if not (flags & SRE_FLAG_VERBOSE) and p.pattern.flags & SRE_FLAG_VERBOSE:
 691         # the VERBOSE flag was switched on inside the pattern.  to be
 692         # on the safe side, we'll parse the whole thing again...
 693         return parse(str, p.pattern.flags)
 694
 695     return p
 696
 697 def parse_template(source, pattern):
 698     # parse 're' replacement string into list of literals and
 699     # group references
 700     s = Tokenizer(source)
 701     sget = s.get
 702     p = []
 703     a = p.append
 704     def literal(literal, p=p, pappend=a):
 705         if p and p[-1][0] is LITERAL:
 706             p[-1] = LITERAL, p[-1][1] + literal
 707         else:
 708             pappend((LITERAL, literal))
 709     sep = source[:0]
 710     if type(sep) is type(""):
 711         makechar = chr
 712     else:
 713         makechar = unichr
 714     while 1:
 715         this = sget()
 716         if this is None:
 717             break # end of replacement string
 718         if this and this[0] == "\\":
 719             # group
 720             c = this[1:2]
 721             if c == "g":
 722                 name = ""
 723                 if s.match("<"):
 724                     while 1:
 725                         char = sget()
 726                         if char is None:
 727                             raise error, "unterminated group name"
 728                         if char == ">":
 729                             break
 730                         name = name + char
 731                 if not name:
 732                     raise error, "bad group name"
 733                 try:
 734                     index = int(name)
 735                     if index < 0:
 736                         raise error, "negative group number"
 737                 except ValueError:
 738                     if not isname(name):
 739                         raise error, "bad character in group name"
 740                     try:
 741                         index = pattern.groupindex[name]
 742                     except KeyError:
 743                         raise IndexError, "unknown group name"
 744                 a((MARK, index))
 745             elif c == "0":
 746                 if s.next in OCTDIGITS:
 747                     this = this + sget()
 748                     if s.next in OCTDIGITS:
 749                         this = this + sget()
 750                 literal(makechar(int(this[1:], 8) & 0xff))
 751             elif c in DIGITS:
 752                 isoctal = False
 753                 if s.next in DIGITS:
 754                     this = this + sget()
 755                     if (c in OCTDIGITS and this[2] in OCTDIGITS and
 756                         s.next in OCTDIGITS):
 757                         this = this + sget()
 758                         isoctal = True
 759                         literal(makechar(int(this[1:], 8) & 0xff))
 760                 if not isoctal:
 761                     a((MARK, int(this[1:])))
 762             else:
 763                 try:
 764                     this = makechar(ESCAPES[this][1])
 765                 except KeyError:
 766                     pass
 767                 literal(this)
 768         else:
 769             literal(this)
 770     # convert template to groups and literals lists
 771     i = 0
 772     groups = []
 773     groupsappend = groups.append
 774     literals = [None] * len(p)
 775     for c, s in p:
 776         if c is MARK:
 777             groupsappend((i, s))
 778             # literal[i] is already None
 779         else:
 780             literals[i] = s
 781         i = i + 1
 782     return groups, literals
 783
 784 def expand_template(template, match):
 785     g = match.group
 786     sep = match.string[:0]
 787     groups, literals = template
 788     literals = literals[:]
 789     try:
 790         for index, group in groups:
 791             literals[index] = s = g(group)
 792             if s is None:
 793                 raise error, "unmatched group"
 794     except IndexError:
 795         raise error, "invalid group reference"
 796     return sep.join(literals)