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- """
- The `compat` module provides support for backwards compatibility with older
- versions of python, and compatibility wrappers around optional packages.
- """
- # flake8: noqa
- import hmac
- import struct
- import sys
- PY3 = sys.version_info[0] == 3
- if PY3:
- text_type = str
- binary_type = bytes
- else:
- text_type = unicode
- binary_type = str
- string_types = (text_type, binary_type)
- try:
- constant_time_compare = hmac.compare_digest
- except AttributeError:
- # Fallback for Python < 2.7
- def constant_time_compare(val1, val2):
- """
- Returns True if the two strings are equal, False otherwise.
- The time taken is independent of the number of characters that match.
- """
- if len(val1) != len(val2):
- return False
- result = 0
- for x, y in zip(val1, val2):
- result |= ord(x) ^ ord(y)
- return result == 0
- # Use int.to_bytes if it exists (Python 3)
- if getattr(int, 'to_bytes', None):
- def bytes_from_int(val):
- remaining = val
- byte_length = 0
- while remaining != 0:
- remaining = remaining >> 8
- byte_length += 1
- return val.to_bytes(byte_length, 'big', signed=False)
- else:
- def bytes_from_int(val):
- buf = []
- while val:
- val, remainder = divmod(val, 256)
- buf.append(remainder)
- buf.reverse()
- return struct.pack('%sB' % len(buf), *buf)
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