What is spec and spec_set

Question

I am using Mock 1.0.1 python.
In the path function definition there are two optional arguments names spec and spec_set (also auto_spec)

patch(target, new=DEFAULT, spec=None, create=False, spec_set=None, autospec=None, new_callable=None, **kwargs)

I have read through the documentation, but find no explanation of them. Maybe they are terms of testing? It will be nice if someone can give information, thank you.

Asked By: Hello lad

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Source

Answer 1

unittest.mock in Python 3.x is basically same with mock.

According to the unittest.mock documentation:

spec: This can be either a list of strings or an existing object (a
class or instance) that acts as the specification for the mock object.
If you pass in an object then a list of strings is formed by calling
dir on the object (excluding unsupported magic attributes and
methods). Accessing any attribute not in this list will raise an
AttributeError.

If spec is an object (rather than a list of strings) then _class_
returns the class of the spec object. This allows mocks to pass
isinstance tests.

spec_set: A stricter variant of spec. If used, attempting to set or
get an attribute on the mock that isn’t on the object passed as
spec_set will raise an AttributeError.

Update Difference between spec and spec_set.

With spec, you can set attribute that is not specified, while with spec_set, it is not allowed to set unspecified attribute.

Example:

>>> from unittest.mock import Mock
>>> class A:
...     def __init__(self, a, b):
...         self.a = a
...         self.b = b
...
>>> aobj = A(1, 2)



>>> m = Mock(spec=aobj)   # spec
>>> m.c   # get -> fail
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/Cellar/python3/3.6.0b4_3/Frameworks/Python.framework/Versions/3.6/lib/python3.6/unittest/mock.py", line 582, in __getattr__
    raise AttributeError("Mock object has no attribute %r" % name)
AttributeError: Mock object has no attribute 'c'
>>> m.c = 9  # set -> success
>>> m.c      # get -> success (although c is not in the spec)
9



>>> m = Mock(spec_set=aobj)   # spec_set
>>> m.a
<Mock name='mock.a' id='4544967400'>
>>> m.b
<Mock name='mock.b' id='4545493928'>
>>> m.c   # get -> fail
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/Cellar/python3/3.6.0b4_3/Frameworks/Python.framework/Versions/3.6/lib/python3.6/unittest/mock.py", line 582, in __getattr__
    raise AttributeError("Mock object has no attribute %r" % name)
AttributeError: Mock object has no attribute 'c'
>>> m.c = 9  # set -> fail
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/Cellar/python3/3.6.0b4_3/Frameworks/Python.framework/Versions/3.6/lib/python3.6/unittest/mock.py", line 688, in __setattr__
    raise AttributeError("Mock object has no attribute '%s'" % name)
AttributeError: Mock object has no attribute 'c'

Answered By: falsetru

Answer 2

You can find more info here: http://www.voidspace.org.uk/downloads/mock-1.0.1.pdf

• spec: This can be either a list of strings or an existing object (a class or instance) that acts as the specification for the mock object. If you pass in an object then a list of strings is formed by calling dir on the object (excluding unsupported magic attributes and methods). Accessing any attribute not in this list will raise an AttributeError. If spec is an object (rather than a list of strings) then class returns the class of the spec object. This allows mocks to pass isinstance tests.

• spec_set: A stricter variant of spec. If used, attempting to set or get an attribute on the mock that isn’t on the object passed as spec_set will raise an AttributeError.

Answered By: rmcc

What is spec and spec_set

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