1 # Copyright 2004-2005 Elemental Security, Inc. All Rights Reserved.

     2 # Licensed to PSF under a Contributor Agreement.

     3 

     4 """Safely evaluate Python string literals without using eval()."""

     5 

     6 import re

     7 

     8 simple_escapes = {"a": "\a",

     9                   "b": "\b",

    10                   "f": "\f",

    11                   "n": "\n",

    12                   "r": "\r",

    13                   "t": "\t",

    14                   "v": "\v",

    15                   "'": "'",

    16                   '"': '"',

    17                   "\\": "\\"}

    18 

    19 def escape(m):

    20     all, tail = m.group(0, 1)

    21     assert all.startswith("\\")

    22     esc = simple_escapes.get(tail)

    23     if esc is not None:

    24         return esc

    25     if tail.startswith("x"):

    26         hexes = tail[1:]

    27         if len(hexes) < 2:

    28             raise ValueError("invalid hex string escape ('\\%s')" % tail)

    29         try:

    30             i = int(hexes, 16)

    31         except ValueError:

    32             raise ValueError("invalid hex string escape ('\\%s')" % tail)

    33     else:

    34         try:

    35             i = int(tail, 8)

    36         except ValueError:

    37             raise ValueError("invalid octal string escape ('\\%s')" % tail)

    38     return chr(i)

    39 

    40 def evalString(s):

    41     assert s.startswith("'") or s.startswith('"'), repr(s[:1])

    42     q = s[0]

    43     if s[:3] == q*3:

    44         q = q*3

    45     assert s.endswith(q), repr(s[-len(q):])

    46     assert len(s) >= 2*len(q)

    47     s = s[len(q):-len(q)]

    48     return re.sub(r"\\(\'|\"|\\|[abfnrtv]|x.{0,2}|[0-7]{1,3})", escape, s)

    49 

    50 def test():

    51     for i in range(256):

    52         c = chr(i)

    53         s = repr(c)

    54         e = evalString(s)

    55         if e != c:

    56             print i, c, s, e

    57 

    58 

    59 if __name__ == "__main__":

    60     test()