Adding module to python at runtime

Question

I have a python script that does this at the begining of the script:

def initialize(module_name):
    return importlib.import_module(module_name) # import module from string

I want to write a test that 'mocks' out the module name like so:

def test():
    # assemble module at run time
    module_obj = {'name': Object, 'another_name': AnotherObject}

    # inject to the "import system"
    inject_mock_module('mymodule', module_obj)

    # assert that the import went correctly
    assert my_module_mock == initialize('mymodule')

How do I do this? First, specifically, how to I create module_obj and how do I define inject_mock_module? This needs to work in both 2.7+ and 3.3+

Are you using Python 2 or 3?

Martijn Pieters
– Martijn Pieters

2013-10-05 18:19:17 +00:00
Commented Oct 5, 2013 at 18:19 — Martijn Pieters
– Martijn Pieters, Commented Oct 5, 2013 at 18:19

Martijn Pieters · Accepted Answer · 2021-03-05 12:33:44Z

3

Use the mock library to mock out the import_module() function. As of Python 3.3, you can import that module as unittest.mock:

try:
    # Python 3.3+
    from unittest.mock import patch
except ImportError:
    # External dependency
    from mock import patch

def test():
    module_obj = {'name': Object, 'another_name': AnotherObject}

    with patch('importlib.import_module', new=module_obj.get):
        assert initialize('name') is module_obj['name']

edited Mar 5, 2021 at 12:33

answered Oct 5, 2013 at 18:28

Martijn Pieters

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2 Comments

Manur Over a year ago

Readers, please note that the second argument to patch() used here is "new", not the more usual "return_value".

Martijn Pieters Over a year ago

@Manur: return_value is not a positional argument in mock.patch(). I've made it more explicit by using new as a keyword argument now, but it would be impossible to pass in return_value as a positional argument anyway.

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