Question

我正在尝试编写一个评估算术表达式的“简单”Python计算器。表达式作为一个字符串（一个程序参数）给出，由操作符（正整数）组成，由运算符（+和 - ）分隔。程序评估表达式并打印出结果。如果提供的参数太多或太少，或者单个程序参数格式错误，程序将打印“ERROR”（不带引号）。一些例子：

python calc.py 09-100-50
-141

python calc.py ""
ERROR

python calc.py 0+45+50-800+-5
ERROR -> gives error because there's a +- combination

python calc.py -1
ERROR

python calc.py 1
1

事情是：我有我的代码，但它没有添加或减去数字，我怎么能检查是否有+ - 组合

import sys
t = len(sys.argv)
num = ""
new_num = 0
if(t > 2 or t == 1):
    print("ERROR")
    exit()
s = sys.argv[1]
new_num_f = 0
if(sys.argv[1] == ""):
    print("ERROR")
    exit()
if(s[0] == "-"):
    print("ERROR")
    exit()
try:
    for i in range(len(s)):
        if(len(s) == 1):
            new_num = s[0]
        elif(str(s[i]) == "+"):
            new_num += int(num)
            num = ""
        elif(s[i] == "-"):
            new_num -= int(num)
            num = ""
        elif(str):
            num += s[i]
    new_num_f = new_num
except(SyntaxError): #this is a wrong error, I don't know what error to use
    print("ERROR")
    exit()
print(str(new_num_f))

如果有人能告诉我如何解决这个问题并解释为什么要使用它，非常感谢

Answer 1

我制作的样式与给定的代码略有不同，但是效果很好。

from sys import argv


def calculate(expression_string):
    expression_length = len(expression_string)
    letter_index = 0

    operands = []
    operators = []

    while letter_index < expression_length:
        if expression_string[letter_index].isdigit():
            operand = ""

            while letter_index < expression_length and expression_string[letter_index].isdigit():
                operand += expression_string[letter_index]
                letter_index += 1

            operands.append(int(operand))
        else:
            operators.append(expression_string[letter_index])

            letter_index += 1

    result = operands.pop(0)

    while operators != []:
        operator = operators.pop(0)

        if operator == "+": result += operands.pop(0)
        elif operator == "-": result -= operands.pop(0)

    return result

def main():
    if len(argv) == 1:
        print("No expression is provided!")
        return

    if list(filter(lambda letter: not letter.isdigit() and letter not in [ "+", "-" ], argv[1])) != []:
        print("Expression should cosist of digits & +, - signs only!")
        return

    operands = argv[1].replace("+", " ").replace("-", " ").split()
    operators = list(filter(lambda letter: not letter.isdigit(), argv[1]))
    if len(operands) - len(operators) != 1:
        print("Expression is incorrect!")
        return

    result = calculate(argv[1])
    print(result)


if __name__ == "__main__":
    main()

python计算器检查sys.argv字符串的+或 -

1 个答案: