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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 get_deployment_timestamp():
 """Returns a unique string represeting the current deployment. Used for busting caches. """

    # TODO: Support other deployment situations.
    if os.environ.get('SERVER_SOFTWARE', '').startswith('Google App Engine'):
        version_id = os.environ.get('CURRENT_VERSION_ID')
        major_version, timestamp = version_id.split('.', 1)
        return timestamp
    return 'test'