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c67b91d046368e91b4adf686fd142a7479483235
[etc/vim.git] / src / 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 from typing import Dict, Match
9
10
11 simple_escapes: Dict[str, str] = {
12     "a": "\a",
13     "b": "\b",
14     "f": "\f",
15     "n": "\n",
16     "r": "\r",
17     "t": "\t",
18     "v": "\v",
19     "'": "'",
20     '"': '"',
21     "\\": "\\",
22 }
23
24
25 def escape(m: Match[str]) -> str:
26     all, tail = m.group(0, 1)
27     assert all.startswith("\\")
28     esc = simple_escapes.get(tail)
29     if esc is not None:
30         return esc
31     if tail.startswith("x"):
32         hexes = tail[1:]
33         if len(hexes) < 2:
34             raise ValueError("invalid hex string escape ('\\%s')" % tail)
35         try:
36             i = int(hexes, 16)
37         except ValueError:
38             raise ValueError("invalid hex string escape ('\\%s')" % tail) from None
39     else:
40         try:
41             i = int(tail, 8)
42         except ValueError:
43             raise ValueError("invalid octal string escape ('\\%s')" % tail) from None
44     return chr(i)
45
46
47 def evalString(s: str) -> str:
48     assert s.startswith("'") or s.startswith('"'), repr(s[:1])
49     q = s[0]
50     if s[:3] == q * 3:
51         q = q * 3
52     assert s.endswith(q), repr(s[-len(q) :])
53     assert len(s) >= 2 * len(q)
54     s = s[len(q) : -len(q)]
55     return re.sub(r"\\(\'|\"|\\|[abfnrtv]|x.{0,2}|[0-7]{1,3})", escape, s)
56
57
58 def test() -> None:
59     for i in range(256):
60         c = chr(i)
61         s = repr(c)
62         e = evalString(s)
63         if e != c:
64             print(i, c, s, e)
65
66
67 if __name__ == "__main__":
68     test()