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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 mean(x, axis=None, keepdims=False):
 """Reduction along axes with mean operation. Args: x (Variable):
 An input variable. axis (None, int or tuple of ints):
 Axis or axes along which mean is calculated. Passing the default value `None` will reduce all dimensions. keepdims (bool):
 Flag whether the reduced axes are kept as a dimension with 1 element. Returns: ~nnabla.Variable: N-D array. """

    from .function_bases import mean as mean_base
    if axis is None:
        axis = range(x.ndim)
    elif not hasattr(axis, '__iter__'):
        axis = [axis]
    return mean_base(x, axis, keepdims)