[issue40864] spec_set/autospec/spec seems to not be reading attributes defined in class body

[Karthikeyan Singaravelan]

Change by Karthikeyan Singaravelan :


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[issue40864] spec_set/autospec/spec seems to not be reading attributes defined in class body

[Evan Fagerberg]

Change by Evan Fagerberg :


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keywords: +patch
pull_requests: +21567
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/22572

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[issue40864] spec_set/autospec/spec seems to not be reading attributes defined in class body

[Evan Fagerberg]

Evan Fagerberg  added the comment:

Reflecting on it more, there should be a sensible way to retrieve the set 
attributes of the init method of any class without explicitly instantiating it, 
via the inspect module.

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[issue40864] spec_set/autospec/spec seems to not be reading attributes defined in class body

[Evan Fagerberg]

Evan Fagerberg  added the comment:

Rereading the documentation, I see that a class attribute set to null will 
return a MagicMock for that attribute. That might be a reasonable workaround. 
Perhaps the more concrete solution would be that dir lists uninitialized class 
attributes and if a type hint is present the class attributes uses a spec of 
that type hint.

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[issue40864] spec_set/autospec/spec seems to not be reading attributes defined in class body

[Karthikeyan Singaravelan]

Karthikeyan Singaravelan  added the comment:

mock uses dir to iterate through the attributes that needs to be specced [0]. 
Unless the variable is initialized it's not listed in dir. Below is an example 
where age is initialized and name is not. name is not present in dir(Person) 
and hence spec will not be able to detect this. This is similar to 
https://bugs.python.org/issue36580.

cat /tmp/baz.py  
class Person:
name: str
age: int = 10

print(dir(Person))
print(Person.name)

python /tmp/baz.py
['__annotations__', '__class__', '__delattr__', '__dict__', '__dir__', 
'__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', 
'__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', 
'__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', 
'__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'age']
Traceback (most recent call last):
  File "/tmp/baz.py", line 6, in 
print(Person.name)
AttributeError: type object 'Person' has no attribute 'name'

[0] 
https://github.com/python/cpython/blob/e005ead49b1ee2b1507ceea94e6f89c28ecf1f81/Lib/unittest/mock.py#L2647

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nosy: +xtreak

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[issue40864] spec_set/autospec/spec seems to not be reading attributes defined in class body

[Evan Fagerberg]

Evan Fagerberg  added the comment:

Sorry one small note, the error in the example happens on
```python
logger.propagate = False
```

and not
```python
assert logger.propagate is False
```

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[issue40864] spec_set/autospec/spec seems to not be reading attributes defined in class body

[Evan Fagerberg]

New submission from Evan Fagerberg :

Hello, I really like that this library allows for really strict mocking however 
one thing I have noticed is that it seems like using spec on a mock does not 
properly read the class body for attributes like some of the documentation 
claims. For example this is a snippet of the Logger class in python 3.6's 
`logging` module
```python
class Logger(Filterer):
name: str
level: int
parent: Union[Logger, PlaceHolder]
propagate: bool
handlers: List[Handler]
disabled: int
```

Now I want to mock that class ensuring that propagate gets set to False for 
example
```python
from unittest import mock
from logging import Logger

logger = mock.Mock(spec_set=Logger)
logger.propagate = False
assert logger.propagate is False
*** AttributeError: Mock object has no attribute 'propagate'
```

I have noticed this does work when the value is initialized in the class body 
so for example

```python
class Logger(Filterer):
name: str
level: int
parent: Union[Logger, PlaceHolder]
propagate: bool = False
handlers: List[Handler]
disabled: int
```

This would not fail with the test in question.

Wondering if this is intended behavior or not or if I am misunderstanding 
something. I have tested this with Python 3.6.10, 3.8.2, all with the same 
result.

--
components: Tests
messages: 370712
nosy: efagerberg
priority: normal
severity: normal
status: open
title: spec_set/autospec/spec seems to not be reading attributes defined in 
class body
type: behavior
versions: Python 3.6, Python 3.8, Python 3.9

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