third_party/cython/src/Cython/Plex/Traditional.py

   1 #=======================================================================
   2 #
   3 #   Python Lexical Analyser
   4 #
   5 #   Traditional Regular Expression Syntax
   6 #
   7 #=======================================================================
   8
   9 from Regexps import Alt, Seq, Rep, Rep1, Opt, Any, AnyBut, Bol, Eol, Char
  10 from Errors import PlexError
  11
  12 class RegexpSyntaxError(PlexError):
  13   pass
  14
  15 def re(s):
  16   """
  17   Convert traditional string representation of regular expression |s|
  18   into Plex representation.
  19   """
  20   return REParser(s).parse_re()
  21
  22 class REParser(object):
  23
  24   def __init__(self, s):
  25     self.s = s
  26     self.i = -1
  27     self.end = 0
  28     self.next()
  29
  30   def parse_re(self):
  31     re = self.parse_alt()
  32     if not self.end:
  33       self.error("Unexpected %s" % repr(self.c))
  34     return re
  35
  36   def parse_alt(self):
  37     """Parse a set of alternative regexps."""
  38     re = self.parse_seq()
  39     if self.c == '|':
  40       re_list = [re]
  41       while self.c == '|':
  42         self.next()
  43         re_list.append(self.parse_seq())
  44       re = Alt(*re_list)
  45     return re
  46
  47   def parse_seq(self):
  48     """Parse a sequence of regexps."""
  49     re_list = []
  50     while not self.end and not self.c in "|)":
  51       re_list.append(self.parse_mod())
  52     return Seq(*re_list)
  53
  54   def parse_mod(self):
  55     """Parse a primitive regexp followed by *, +, ? modifiers."""
  56     re = self.parse_prim()
  57     while not self.end and self.c in "*+?":
  58       if self.c == '*':
  59         re = Rep(re)
  60       elif self.c == '+':
  61         re = Rep1(re)
  62       else: # self.c == '?'
  63         re = Opt(re)
  64       self.next()
  65     return re
  66
  67   def parse_prim(self):
  68     """Parse a primitive regexp."""
  69     c = self.get()
  70     if c == '.':
  71       re = AnyBut("\n")
  72     elif c == '^':
  73       re = Bol
  74     elif c == '$':
  75       re = Eol
  76     elif c == '(':
  77       re = self.parse_alt()
  78       self.expect(')')
  79     elif c == '[':
  80       re = self.parse_charset()
  81       self.expect(']')
  82     else:
  83       if c == '\\':
  84         c = self.get()
  85       re = Char(c)
  86     return re
  87
  88   def parse_charset(self):
  89     """Parse a charset. Does not include the surrounding []."""
  90     char_list = []
  91     invert = 0
  92     if self.c == '^':
  93       invert = 1
  94       self.next()
  95     if self.c == ']':
  96       char_list.append(']')
  97       self.next()
  98     while not self.end and self.c != ']':
  99       c1 = self.get()
 100       if self.c == '-' and self.lookahead(1) != ']':
 101         self.next()
 102         c2 = self.get()
 103         for a in xrange(ord(c1), ord(c2) + 1):
 104           char_list.append(chr(a))
 105       else:
 106         char_list.append(c1)
 107     chars = ''.join(char_list)
 108     if invert:
 109       return AnyBut(chars)
 110     else:
 111       return Any(chars)
 112
 113   def next(self):
 114     """Advance to the next char."""
 115     s = self.s
 116     i = self.i = self.i + 1
 117     if i < len(s):
 118       self.c = s[i]
 119     else:
 120       self.c = ''
 121       self.end = 1
 122
 123   def get(self):
 124     if self.end:
 125       self.error("Premature end of string")
 126     c = self.c
 127     self.next()
 128     return c
 129
 130   def lookahead(self, n):
 131     """Look ahead n chars."""
 132     j = self.i + n
 133     if j < len(self.s):
 134       return self.s[j]
 135     else:
 136       return ''
 137
 138   def expect(self, c):
 139     """
 140     Expect to find character |c| at current position.
 141     Raises an exception otherwise.
 142     """
 143     if self.c == c:
 144       self.next()
 145     else:
 146       self.error("Missing %s" % repr(c))
 147
 148   def error(self, mess):
 149     """Raise exception to signal syntax error in regexp."""
 150     raise RegexpSyntaxError("Syntax error in regexp %s at position %d: %s" % (
 151       repr(self.s), self.i, mess))
 152
 153
 154