jenkins.Jenkins.build_job doesn't use server URL specified when the object is created.

Ubuntu 16.04, python 3.5.2, python-jenkins is pip installed latest, but I can't get the version number due to errors using pbr.version.VersionInfo('jenkins').

    jenk = jenkins.Jenkins(server_url, username='****', password=token)
    try:
        jenk.build_job('testing_pipe',
                       {'git_sha':git_sha,
                        'module_name':module,
                        'params_name':params},
                       {'token':'build'})

reports: "unknown url type: 'job/testing_pipe/<etc>'"

Why is it not using my specified server_url? It is a computer in the local network.