# Copyright 2004-2005 Elemental Security, Inc. All Rights Reserved.
# Licensed to PSF under a Contributor Agreement.

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

import re

simple_escapes = {"a": "\a",
"b": "\b",
"f": "\f",
"n": "\n",
"r": "\r",
"t": "\t",
"v": "\v",
"'": "'",
'"': '"',
"\\": "\\"}

def escape(m):
all, tail = m.group(0, 1)
assert all.startswith("\\")
esc = simple_escapes.get(tail)
if esc is not None:
return esc
if tail.startswith("x"):
hexes = tail[1:]
if len(hexes) < 2:
raise ValueError("invalid hex string escape ('\\%s')" % tail)
try:
i = int(hexes, 16)
except ValueError:
raise ValueError("invalid hex string escape ('\\%s')" % tail)
else:
try:
i = int(tail, 8)
except ValueError:
raise ValueError("invalid octal string escape ('\\%s')" % tail)
return chr(i)

def evalString(s):
assert s.startswith("'") or s.startswith('"'), repr(s[:1])
q = s[0]
if s[:3] == q*3:
q = q*3
assert s.endswith(q), repr(s[-len(q):])
assert len(s) >= 2*len(q)
s = s[len(q):-len(q)]
return re.sub(r"\\(\'|\"|\\|[abfnrtv]|x.{0,2}|[0-7]{1,3})", escape, s)

def test():
for i in range(256):
c = chr(i)
s = repr(c)
e = evalString(s)
if e != c:
print i, c, s, e


if __name__ == "__main__":
test()