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bpo-32092: Mock patch fix autospec by claudiubelu · Pull Request #4476 · python/cpython

@claudiubelu claudiubelu changed the title Mock patch fix autospec bpo-32092: Mock patch fix autospec

Nov 20, 2017 
Mock can accept an spec object / class as argument, making sure
that accessing attributes that do not exist in the spec will cause an
AttributeError to be raised, but there is no guarantee that the spec's
methods signatures are respected in any way. This creates the possibility
to have faulty code with passing unittests and assertions.

Example:

from unittest import mock

class Something(object):
    def foo(self, a, b, c, d):
        pass

m = mock.Mock(spec=Something)
m.foo()

Adds the autospec argument to Mock, and its mock_add_spec method.

Passes the spec's attribute with the same name to the child mock (spec-ing
the child), if the mock's autospec is True.

Sets _mock_check_sig if the given spec is callable.

Adds unit tests to validate the fact that the autospec method signatures are
respected.
Currently, when patching methods with autospec, their self / cls
arguments are not consumed, causing call asserts to fail (they
expect an instance / class reference as the first argument).

Example:

from unittest import mock

class Something(object):
    def foo(self, a, b, c, d):
        pass

patcher = mock.patch.object(Something, 'foo', autospec=True)
patcher.start()

s = Something()
s.foo()

@bclau bclau mannequin mentioned this pull request

Apr 10, 2022

stephenfin added a commit to stephenfin/cpython that referenced this pull request

Mar 27, 2026 
Currently, when patching instance / class methods with autospec, their
self / cls arguments are not consumed, causing call asserts to fail
(they expect an instance / class reference as the first argument).
Example:

  from unittest import mock

  class Something(object):
      def foo(self, a, b, c, d):
          pass

  with mock.patch.object(Something, 'foo', autospec=True):
      s = Something()
      s.foo()

Fix this by skipping the first argument when presented with a method.

Based on python#4476

Signed-off-by: Stephen Finucane <stephen@that.guru>
Co-authored-by: Claudiu Belu <cbelu@cloudbasesolutions.com>

stephenfin added a commit to stephenfin/cpython that referenced this pull request

Mar 27, 2026 
Currently, when patching instance / class methods with autospec, their
self / cls arguments are not consumed, causing call asserts to fail
(they expect an instance / class reference as the first argument).
Example:

  from unittest import mock

  class Something(object):
      def foo(self, a, b, c, d):
          pass

  with mock.patch.object(Something, 'foo', autospec=True):
      s = Something()
      s.foo()

Fix this by skipping the first argument when presented with a method.

Based on python#4476

Signed-off-by: Stephen Finucane <stephen@that.guru>
Co-authored-by: Claudiu Belu <cbelu@cloudbasesolutions.com>