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python - 在 Python 中将字符串转换为整数表达式

问题描述

假设我有一个这样的字符串：

"(((((908488990) - (255272197)) + ((-287634246) - (1144917742))) + (((1178779462) + (1410551276)) - ((-244815224) - (-722994984)))) + ((((-1134622847) - (-818189911)) + ((-479615696) + (-938948012))) + (((-1762293529) + (1281608170)) - ((1468184728) + (-895014314)))))"

如何在 Python 中将其转换为这样的表达式（不带引号）：

(((((908488990) - (255272197)) + ((-287634246) - (1144917742))) + (((1178779462) + (1410551276)) - ((-244815224) - (-722994984)))) + ((((-1134622847) - (-818189911)) + ((-479615696) + (-938948012))) + (((-1762293529) + (1281608170)) - ((1468184728) + (-895014314)))))

这样我就可以得到该表达式的结果：

-1457036634

标签： python

解决方案

如果您想处理@Hymns-For-Disco 提到的用户输入中的字符串，使用 eval 可能会很危险。

这是一个关于如何处理此类字符串的示例，它有点长，部分可以放在子函数中，但它给出了正确的输出（加上括号检查）：

test_string = r"(((((908488990) - (255272197)) + ((-287634246) - (1144917742))) + (((1178779462) + (1410551276)) - ((-244815224) - (-722994984)))) + ((((-1134622847) - (-818189911)) + ((-479615696) + (-938948012))) + (((-1762293529) + (1281608170)) - ((1468184728) + (-895014314)))))"


import operator
operators = {'+' : operator.add, '-' : operator.sub} # you can add other operators here like operator.multiply

def compute(string):
    operator = None
    value_left = None

    it = iter(string) 
    while True:
        try:
            character = next(it)
        except StopIteration:
            break 
        if character ==' ': continue
        if character == '(':
            count = 1 #count open parenthesis
            sub_string = ''
            while True:
                try:
                    character = next(it)
                except StopIteration:
                    raise(EOFError("Not matching parenthesis"))
                if character == '(':
                    count+=1
                if character == ')':
                    if count == 1:
                        break
                    else:
                        sub_string+= character
                        count-=1
                else:
                    sub_string+= character
            if operator is None:
                print('call compute with{}'.format(sub_string))
                value_left = compute(sub_string)
                continue
            else:
                return operator(value_left,compute(sub_string))

        if character.isdigit():
            temp_num = character
            while character.isdigit() or character=='.':
                try:
                    character = next(it)
                except StopIteration:
                    break
                temp_num+= character
            if operator is None:
                value_left = float(temp_num)
            else:
                return operator(value_left, float(temp_num))
        if character in operators.keys():
            operator = operators[character]
            #test for unary '-' operator:
            if character == '-' and value_left is None:
                value_left = 0.0
    return value_left


print(compute(test_string)) #returns -1457036634.0

test_string =r'(3+4'
print(compute(test_string)) # raises EOFError: Not matching parenthesis

希望对你有帮助

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