def get_meter(name: str, key: str) -> Meter:
    """Get a single Meter instance aggregated under *name* and *key*.

    Returns:
        Meter or None if no metrics have been logged under *name* and *key*.
    """
    if name not in _aggregators:
        return None
    return _aggregators[name].get(key, None)
Get a single Meter instance aggregated under *name* and *key*.

Returns:
Meter or None if no metrics have been logged under *name* and *key*.
fairseq/logging/metrics.py