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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_environ(environ):
 # type: (Dict[str, str]) -> Iterator[Tuple[str, str]] """ Returns our whitelisted environment variables. """

    keys = ["SERVER_NAME", "SERVER_PORT"]
    if _should_send_default_pii():
        # Add all three headers here to make debugging of proxy setup easier.
        keys += ["REMOTE_ADDR", "HTTP_X_FORWARDED_FOR", "HTTP_X_REAL_IP"]

    for key in keys:
        if key in environ:
            yield key, environ[key]