SimpleCalc.py 文件源码

def evaluateStack( s ):
    op = s.pop()
    if op == 'unary -':
        return -evaluateStack( s )
    if op in "+-*/^":
        op2 = evaluateStack( s )
        op1 = evaluateStack( s )
        return opn[op]( op1, op2 )
    elif op == "PI":
        return math.pi # 3.1415926535
    elif op == "E":
        return math.e  # 2.718281828
    elif op in fn:
        return fn[op]( evaluateStack( s ) )
    elif op[0].isalpha():
        if op in variables:
            return variables[op]
        raise Exception("invalid identifier '%s'" % op)
    else:
        return float( op )