code: def max_site_coordination_numbers( self ):
          
          return { l : max( c ) for l, c in self.site_coordination_numbers().items() }
docs: Returns a dictionary of the maximum coordination number for each site label.
          e.g.::
     
              { 'A' : 4, 'B' : 4 }
  
          Args:
              none
  
          Returns:
              max_coordination_numbers (Dict(Str:Int)): dictionary of maxmimum coordination
                                                        number for each site label.