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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def jenkins_last_build_sha():
 """ Returns the sha of the last completed jenkins build for this project. Expects JOB_URL in environment """

        job_url = os.getenv('JOB_URL')
        job_json_url = "{0}/api/json".format(job_url)
        response = urllib.urlopen(job_json_url)
        job_data = json.loads(response.read())

        last_completed_build_url = job_data['lastCompletedBuild']['url']
        last_complete_build_json_url = "{0}/api/json".format(last_completed_build_url)

        response = urllib.urlopen(last_complete_build_json_url)
        last_completed_build = json.loads(response.read())

        return last_completed_build[1]['lastBuiltRevision']['SHA1']