Actual method to read Redis settings from app configuration and initialize the StrictRedis instance.

        Positional arguments:
        app -- Flask application instance.
        config_prefix -- Prefix used in config key names in the Flask app's configuration. Useful for applications which
            interface with more than one Redis server. Default value is 'REDIS'. Will be converted to upper case (e.g.
            'REDIS_CACHE').
            Examples:
              REDIS_URL = 'redis://localhost/0'
              REDIS_CACHE_URL = 'redis://localhost/1'

def init_app(self, app, config_prefix=None):
        """Actual method to read Redis settings from app configuration and initialize the StrictRedis instance.

        Positional arguments:
        app -- Flask application instance.
        config_prefix -- Prefix used in config key names in the Flask app's configuration. Useful for applications which
            interface with more than one Redis server. Default value is 'REDIS'. Will be converted to upper case (e.g.
            'REDIS_CACHE').
            Examples:
              REDIS_URL = 'redis://localhost/0'
              REDIS_CACHE_URL = 'redis://localhost/1'
        """
        # Normalize the prefix and add this instance to app.extensions.
        config_prefix = (config_prefix or 'REDIS').rstrip('_').upper()
        if not hasattr(app, 'extensions'):
            app.extensions = dict()
        if config_prefix.lower() in app.extensions:
            raise ValueError('Already registered config prefix {0!r}.'.format(config_prefix))
        app.extensions[config_prefix.lower()] = _RedisState(self, app)

        # Read config.
        args = read_config(app.config, config_prefix)

        # Instantiate StrictRedis.
        super(Redis, self).__init__(**args)