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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 api_key(value=None):
 """Set or get the API key. Also set via environment variable GRAPHISTRY_API_KEY."""


        if value is None:
            return PyGraphistry._config['api_key']

        # setter
        if value is not PyGraphistry._config['api_key']:
            PyGraphistry._config['api_key'] = value.strip()
            PyGraphistry._is_authenticated = False