[issue30587] Mock with spec object does not ensure method call signatures

[Ben Reilly]

Change by Ben Reilly :


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nosy: +breilly_box

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[issue30587] Mock with spec object does not ensure method call signatures

[Phil Connell]

Change by Phil Connell :


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nosy: +pconnell

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[issue30587] Mock with spec object does not ensure method call signatures

[Michael Foord]

Michael Foord  added the comment:

This will affect spec and spec_set.

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[issue30587] Mock with spec object does not ensure method call signatures

[Michael Foord]

Michael Foord  added the comment:

I'd like spec to have signature validation. I don't think the use case for 
"attribute validation only" (current spec behaviour) is very strong and I'd 
rather not add new keywords. The mock API is already too complex.

I'll take the existing PR and modify it to use spec instead of adding the new 
autospec.

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[issue30587] Mock with spec object does not ensure method call signatures

[Michael Foord]

Michael Foord  added the comment:

Spec objects are currently dumb. It would be a new feature to add signature 
validation to them. 

I think it would be a useful feature though as currently autospec sort of 
obsoletes spec objects whilst being more heavyweight and harder to use. 

I think it would appropriate to add to 3.8 but not to 3.7. 

Compatibility with existing tests is the issue. The obvious answer is a flag to 
turn it on/off but that adds complexity to the API. 

My gut feeling is that spec objects are far more commonly used in situations 
where validation would be useful than a detriment. 

> On 31 Mar 2019, at 18:07, Karthikeyan Singaravelan  
> wrote:
> 
> 
> Karthikeyan Singaravelan  added the comment:
> 
> I am slightly concerned if spec should gain more responsibility than just 
> validating attribute access which is mentioned in the docs. With the linked 
> PR spec below would also validate the signature which is not done in Python 
> 3.7 so this might break code for someone who only wants to validate access 
> attribute access and not signature of the methods. It seems the PR also adds 
> autospec argument to Mock that is currently not supported though spec and 
> spec_set are supported.
> 
> from unittest import mock
> 
> def foo(lish):
>pass
> 
> mock_foo = mock.Mock(spec=foo)
> mock_foo(1, 2)
> 
> try:
>mock_foo.non_existent
> except AttributeError:
>print("raises AttributeError for non-existent attribute")
> 
> # 3.7
> 
> ➜  cpython git:(pr_1982) python3.7 /tmp/foo.py
> raises AttributeError for non-existent attribute
> 
> # With PR
> 
> ➜  cpython git:(pr_1982) ./python.exe /tmp/foo.py
> Traceback (most recent call last):
>  File "/tmp/foo.py", line 7, in 
>mock_foo(1, 2)
>  File 
> "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/unittest/mock.py", 
> line 1009, in __call__
>_mock_self._mock_check_sig(*args, **kwargs)
>  File 
> "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/unittest/mock.py", 
> line 103, in checksig
>sig.bind(*args, **kwargs)
>  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/inspect.py", 
> line 3016, in bind
>return args[0]._bind(args[1:], kwargs)
>  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/inspect.py", 
> line 2937, in _bind
>raise TypeError('too many positional arguments') from None
> TypeError: too many positional arguments
> 
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> 
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[issue30587] Mock with spec object does not ensure method call signatures

[Karthikeyan Singaravelan]

Change by Karthikeyan Singaravelan :


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pull_requests:  -4411

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[issue30587] Mock with spec object does not ensure method call signatures

[Karthikeyan Singaravelan]

Karthikeyan Singaravelan  added the comment:

I am slightly concerned if spec should gain more responsibility than just 
validating attribute access which is mentioned in the docs. With the linked PR 
spec below would also validate the signature which is not done in Python 3.7 so 
this might break code for someone who only wants to validate access attribute 
access and not signature of the methods. It seems the PR also adds autospec 
argument to Mock that is currently not supported though spec and spec_set are 
supported.

from unittest import mock

def foo(lish):
pass

mock_foo = mock.Mock(spec=foo)
mock_foo(1, 2)

try:
mock_foo.non_existent
except AttributeError:
print("raises AttributeError for non-existent attribute")

# 3.7

➜  cpython git:(pr_1982) python3.7 /tmp/foo.py
raises AttributeError for non-existent attribute

# With PR

➜  cpython git:(pr_1982) ./python.exe /tmp/foo.py
Traceback (most recent call last):
  File "/tmp/foo.py", line 7, in 
mock_foo(1, 2)
  File 
"/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/unittest/mock.py", 
line 1009, in __call__
_mock_self._mock_check_sig(*args, **kwargs)
  File 
"/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/unittest/mock.py", 
line 103, in checksig
sig.bind(*args, **kwargs)
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/inspect.py", 
line 3016, in bind
return args[0]._bind(args[1:], kwargs)
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/inspect.py", 
line 2937, in _bind
raise TypeError('too many positional arguments') from None
TypeError: too many positional arguments

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[issue30587] Mock with spec object does not ensure method call signatures

[Karthikeyan Singaravelan]

Change by Karthikeyan Singaravelan :


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nosy: +xtreak

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[issue30587] Mock with spec object does not ensure method call signatures

[Karthikeyan Singaravelan]

Change by Karthikeyan Singaravelan :


--
nosy: +cjw296, mariocj89, michael.foord
versions: +Python 3.8 -Python 2.7, Python 3.3, Python 3.4, Python 3.5, Python 
3.6, Python 3.7

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[issue30587] Mock with spec object does not ensure method call signatures

[Claudiu Belu]

Change by Claudiu Belu :


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keywords: +patch
pull_requests: +4411
stage:  -> patch review

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[issue30587] Mock with spec object does not ensure method call signatures

[Claudiu Belu]

New submission from Claudiu Belu:

Mock can accept a 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.

Steps to reproduce:

>>> import mock
>>>
>>> class Something(object):
... def foo(self, a, b, c, d):
... pass
...
>>>
>>> m = mock.Mock(spec=Something)
>>> m.foo()

>>> # TypeError should be raised, but it isn't.
...
>>> m.foo.assert_called_once_with()


Expected behaviour: It should have raised a TypeError, since the method 
signature is: def meth(self, a, b, c, d):

Actual behaviour: No error.

--
components: Library (Lib)
messages: 295335
nosy: cbelu
priority: normal
pull_requests: 2051
severity: normal
status: open
title: Mock with spec object does not ensure method call signatures
type: behavior
versions: Python 2.7, Python 3.3, Python 3.4, Python 3.5, Python 3.6, Python 3.7

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