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import decimal
import hmac
import numbers
import sys
PY2 = sys.version_info[0] == 2
if PY2:
from itertools import izip
text_type = unicode # noqa: 821
else:
izip = zip
text_type = str
number_types = (numbers.Real, decimal.Decimal)
def _constant_time_compare(val1, val2):
"""Return ``True`` if the two strings are equal, ``False``
otherwise.
The time taken is independent of the number of characters that
match. Do not use this function for anything else than comparision
with known length targets.
This is should be implemented in C in order to get it completely
right.
This is an alias of :func:`hmac.compare_digest` on Python>=2.7,3.3.
"""
len_eq = len(val1) == len(val2)
if len_eq:
result = 0
left = val1
else:
result = 1
left = val2
for x, y in izip(bytearray(left), bytearray(val2)):
result |= x ^ y
return result == 0
# Starting with 2.7/3.3 the standard library has a c-implementation for
# constant time string compares.
constant_time_compare = getattr(hmac, "compare_digest", _constant_time_compare)
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