def mw(self):
        """Molecular weight"""
        m = P_TAB[self.symbol].get('std_weight')
        mh = P_TAB['H'].get('std_weight')
        return m + mh * self.H_count
def mw ( self ) : m = P_TAB [ self . symbol ] . get ( 'std_weight' ) mh = P_TAB [ 'H' ] . get ( 'std_weight' ) return m + mh * self . H_count
Molecular weight