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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 signup(remote_app):
 """Extra signup step."""

    if remote_app not in current_oauthclient.signup_handlers:
        return abort(404)
    res = current_oauthclient.signup_handlers[remote_app]['view']()
    return abort(404) if res is None else res