The patch looks good, thank you. Please fix the pep8 failure and I'll merge.

It didn't work =(

I tried:

    project.only_allow_merge_if_build_succeeds = True
    project.save()

and

    project.only_allow_merge_if_build_succeeds = 1
    project.save()

but none worked.

Am I doing something wrong?

I tested here and everything seems to work, using a boolean value. Are you sure that your gitlab version support this attribute? It's recent.

I can set this value using the GUI, but I'm not sure about the API support.

Since I'm no Python developer, I may have done something wrong. Here is what I did:

$ sudo pip uninstall python-gitlab
$ git clone https://github.com/gpocentek/python-gitlab.git
$ cd python-gitlab
$ python setup.py install

Does this suffice to use the newest version containing the change introduced in this MR?

Yes you should be able to use your change. Do you know the version of the gitlab server?

From what I see in the git log you need gitlab 8.12 to get this feature in the API.

We are using GitLab Community Edition 8.9.0.

I'll try to update and give you some input again.