code: def add_dr( self, dr ):
           
          this_bin = int( dr / self.dr ) 
          if this_bin > self.number_of_bins:
              raise IndexError( 'dr is larger than rdf max_r' )
          self.data[ this_bin ] += 1
docs: Add an observed interatomic distance to the g(r) data at dr.
  
          Args:
              dr (Float): the interatomic distance, dr.
  
          Returns:
              None