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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:
# Importing ABCs from collections will be removed in PY3.8
from collections.abc import Iterable, Mapping
except ImportError:
from collections import Iterable, Mapping
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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