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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 _configure_from_mapping(self, item, whitelist_keys=False, whitelist=None):
 """Configure from a mapping, or dict, like object. Args: item (dict):
 A dict-like object that we can pluck values from. Keyword Args: whitelist_keys (bool):
 Should we whitelist the keys before adding them to the configuration? If no whitelist is provided, we use the pre-existing config keys as a whitelist. whitelist (list[str]):
 An explicit list of keys that should be allowed. If provided and ``whitelist_keys`` is true, we will use that as our whitelist instead of pre-existing app config keys. Returns: fleaker.App: Returns itself. """

        if whitelist is None:
            whitelist = self.config.keys()

        if whitelist_keys:
            item = {k: v for k, v in item.items() if k in whitelist}

        self.config.from_mapping(item)

        return self