Mock patching from/import statement in Python

Question

I am trying to get mock.patch to work on the following piece of sample code:

from mock import patch from collections import defaultdict  with patch('collections.defaultdict'):   d = defaultdict()   print 'd:', d 

This outputs the following:

d: defaultdict(None, {}) 

Which means that defaultdict was not patched.

If I replace the from/import statement with a straight import statement it works:

from mock import patch import collections  with patch('collections.defaultdict'):  d = collections.defaultdict()  print 'd:', d 

Output is:

d: <MagicMock name='defaultdict()' id='139953944084176'> 

Is there any way to patch a call using from/import?

Thank you

Answer 1

If you're patching something in the same module, you can use __main__:

from mock import patch from collections import defaultdict  with patch('__main__.defaultdict'):     d = defaultdict()     print 'd:', d 

If you're mocking something for an imported module, however, you'll want to use that module's name so the correct reference (or name) is patched:

# foo.py  from collections import defaultdict  def bar():     return defaultdict()   # foo_test.py      from mock import patch from foo import bar  with patch('foo.defaultdict'):     print bar() 

The point here is that patch wants the full path to the thing it is patching. This just looks a little weird when patching something in the current module, since folks don't often use __main__ (or have to refer to the current module, for that matter).

Answer 2

patch works by patching names. You can't achieve anything by patching the name collections.defaultdict if you are using the name defaultdict (in the local namespace) to access the object. See the documentation at https://docs.python.org/3/library/unittest.mock.html#where-to-patch