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

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# Licensed to PSF under a Contributor Agreement.

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

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import re

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

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"b": "\b",

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"f": "\f",

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"n": "\n",

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"r": "\r",

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"t": "\t",

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"v": "\v",

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"'": "'",

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'"': '"',

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"\\": "\\"}

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def escape(m):

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

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assert all.startswith("\\")

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esc = simple_escapes.get(tail)

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if esc is not None:

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return esc

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if tail.startswith("x"):

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hexes = tail[1:]

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if len(hexes) < 2:

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

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try:

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i = int(hexes, 16)

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except ValueError:

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

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else:

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try:

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i = int(tail, 8)

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except ValueError:

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

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return chr(i)

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def evalString(s):

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

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q = s[0]

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

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q = q*3

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

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

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

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

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def test():

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for i in range(256):

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c = chr(i)

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s = repr(c)

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e = evalString(s)

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if e != c:

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print i, c, s, e

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if __name__ == "__main__":

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test()

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