Lib/lib2to3/pgen2/literals.py

   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()