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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_callback_context(env):
 """return whether the current callback context is cv or train"""

    if env.model is not None and env.cvfolds is None:
        context = 'train'
    elif env.model is None and env.cvfolds is not None:
        context = 'cv'
    return context