Python monkeypatch doesn't patch function correctly

I'm trying to use monkeypatch to mock one public function but it doesn't seem to work for me.

Here's my test

mp = monkeypatch()
mp.setattr(mrss.version_controller, 'get_version', lambda env: 7)
mrss_feed = get_feed(env=get_config())

And this is my get_feed function

from mrss.version_controller import get_version

def get_feed(env=os.environ):
    uploader = Uploader(env=env)
    folder = env.get('S3_FOLDER')

    version = get_version(env)
    print version.isdigit()
    print 'version is {v}'.format(v=str(version))
    if not version or not version.isdigit():
        return ''

And all I got for get_version is empty string

False
version is