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[etc/vim.git] / blib2to3 / 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) from None
33     else:
34         try:
35             i = int(tail, 8)
36         except ValueError:
37             raise ValueError("invalid octal string escape ('\\%s')" % tail) from None
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()