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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 sphere(target, pore_diameter='pore.diameter'):
 r""" Calculate pore volume from diameter assuming a spherical pore body Parameters target : OpenPNM Object The object which this model is associated with. This controls the length of the calculated array, and also provides access to other necessary geometric properties. pore_diameter : string The dictionary key of the pore diameter values """

    diams = target[pore_diameter]
    value = _pi/6*diams**3
    return value