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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 create_credentials(credentials_file=None, service_email=None, service_key=None, scope='https://www.googleapis.com/auth/androidpublisher'):
 """ Create Google credentials object. If given credentials_file is None, try to retrieve file path from environment or look up file in homefolder. """

    credentials = None
    if service_email is None and service_key is None:
        print(credentials_file)
        if credentials_file is None:
            # try load file from env
            key = 'PLAY_DELIVER_CREDENTIALS'
            if key in os.environ:
                credentials_file = os.environ[key]

        if credentials_file is None:
            # try to find the file in home
            path = os.path.expanduser('~/.playdeliver/credentials.json')
            if os.path.exists(path):
                credentials_file = path

        if credentials_file is not None:
            credentials = client.GoogleCredentials.from_stream(
                credentials_file)
            credentials = credentials.create_scoped(scope)
        else:
            sys.exit("no credentials")
    else:
        credentials = client.SignedJwtAssertionCredentials(
            service_email, _load_key(service_key), scope=scope)
    return credentials