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.. hazmat::
MultiBackend
============
.. currentmodule:: cryptography.hazmat.backends.multibackend
.. class:: MultiBackend(backends)
.. versionadded:: 0.2
This class allows you to combine multiple backends into a single backend
that offers the combined features of all of its constituents.
.. testsetup::
from cryptography import utils
from cryptography.exceptions import UnsupportedAlgorithm, _Reasons
from cryptography.hazmat.backends.interfaces import HashBackend
from cryptography.hazmat.backends.openssl.backend import backend as backend2
@utils.register_interface(HashBackend)
class DummyHashBackend(object):
def hash_supported(self, algorithm):
return False
def create_hash_ctx(self, algorithm):
raise UnsupportedAlgorithm("", _Reasons.UNSUPPORTED_HASH)
backend1 = DummyHashBackend()
.. doctest::
>>> from cryptography.hazmat.backends.multibackend import MultiBackend
>>> from cryptography.hazmat.primitives import hashes
>>> backend1.hash_supported(hashes.SHA256())
False
>>> backend2.hash_supported(hashes.SHA256())
True
>>> multi_backend = MultiBackend([backend1, backend2])
>>> multi_backend.hash_supported(hashes.SHA256())
True
:param backends: A ``list`` of backend objects. Backends are checked for
feature support in the order they appear in this list.
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