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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 _make_3d(field, twod):
 """Add a dimension to field if necessary. Args: field (numpy.array):
 the field that need to be 3d. twod (str):
 'XZ', 'YZ' or None depending on what is relevant. Returns: numpy.array: reshaped field. """

    shp = list(field.shape)
    if twod and 'X' in twod:
        shp.insert(1, 1)
    elif twod:
        shp.insert(0, 1)
    return field.reshape(shp)