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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 dr( self, atom1, atom2 ):
 """ Calculate the distance between two atoms. Args: atom1 (vasppy.Atom):
 Atom 1. atom2 (vasppy.Atom):
 Atom 2. Returns: (float):
 The distance between Atom 1 and Atom 2. """

        return self.cell.dr( atom1.r, atom2.r )