pythonunit-testingmockingmagicmock

mock file open in python

I'm trying to mock file open, and all of the examples show that I need to 

@patch('open', create=True)

but I keep getting 

Need a valid target to patch. You supplied: 'open'

I know patch needs the full dotted path of open, but I have no idea what it is. As a matter of fact, I'm not even sure that's the problem.

Solution

  • You need to include a module name; if you are testing in a script, the name of the module is __main__:

    @patch('__main__.open')

    otherwise use the name of the module that contains the code you are testing:

    @patch('module_under_test.open')

    so that any code that uses the open() built-in will find the patched global instead.

    Note that the mock module comes with a mock_open() utility that'll let you build a suitable open() call with file data:

    @patch('__main__.open', mock_open(read_data='foo\nbar\nbaz\n'))