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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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