(p)
assignment_list : ID "=" expression
                    |   assignment_list "," ID "=" expression
assignment_list : ID "=" expression
                    |   assignment_list "," ID "=" expression
assignment_list : ID = expression | assignment_list ID = expression
def p_assignment_list(p):
    '''assignment_list : ID "=" expression
                    |   assignment_list "," ID "=" expression
       '''
def p_assignment_list ( p ) :