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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_model_from_key(key):
 """Gets the model from a given key."""

    _known_models = {}
    model_name = key.split(':', 2)[0]
    # populate
    for klass in Model.__subclasses__():
        _known_models[klass.__name__] = klass
    return _known_models.get(model_name, None)