Returns True if this is the "first" call for a given key.

    Various logging settings can adjust the definition of "first".

    Example:
        >>> if log_once("some_key"):
        ...     logger.info("Some verbose logging statement")

def log_once(key):
    """Returns True if this is the "first" call for a given key.

    Various logging settings can adjust the definition of "first".

    Example:
        >>> if log_once("some_key"):
        ...     logger.info("Some verbose logging statement")
    """

    global _last_logged

    if _disabled:
        return False
    elif key not in _logged:
        _logged.add(key)
        _last_logged = time.time()
        return True
    elif _periodic_log and time.time() - _last_logged > 60.0:
        _logged.clear()
        _last_logged = time.time()
        return False
    else:
        return False