Python实现简单的计算器

需求描述：

1、实现加减乘除及拓号优先级解析

2、用户输入 1 - 2 * ( (60-30 +(-40/5) * (9-2*5/3 + 7 /3*99/4*2998 +10 * 568/14 )) - (-4*3)/ (16-3*2) )等类似公式后，必须自己解析里面的(),+,-,*,/符号和公式，运算后得出结果

实现代码：

  1 import re
  2 import functools
  3
  4
  5 def minus_operator_handler(formula):
  6     ‘‘‘处理一些特殊的减号运算‘‘‘
  7     minus_operators = re.split("-",formula)
  8     calc_list= re.findall("[0-9]",formula)
  9     if minus_operators[0] == ‘‘: #第一值肯定是负号
 10         calc_list[0] = ‘-%s‘ % calc_list[0]
 11     res = functools.reduce(lambda x,y:float(x) - float(y), calc_list)
 12     print("\033[33;1m减号[%s]处理结果:\033[0m" % formula, res )
 13     return res
 14
 15 def remove_duplicates(formula):
 16     formula = formula.replace("++","+")
 17     formula = formula.replace("+-","-")
 18     formula = formula.replace("-+","-")
 19     formula = formula.replace("--","+")
 20     formula = formula.replace("- -","+")
 21     return formula
 22 def compute_mutiply_and_dividend(formula):
 23     ‘‘‘算乘除,传进来的是字符串噢‘‘‘
 24     operators = re.findall("[*/]", formula )
 25     calc_list = re.split("[*/]", formula )
 26     res = None
 27     for index,i in enumerate(calc_list):
 28         if res:
 29             if operators[index-1] == "*":
 30                 res *= float(i)
 31             elif operators[index-1] == "/":
 32                 res /= float(i)
 33         else:
 34             res = float(i)
 35
 36     print("\033[31;1m[%s]运算结果=\033[0m" %formula, res  )
 37     return res
 38 def handle_minus_in_list(operator_list,calc_list):
 39     ‘‘‘有的时候把算术符和值分开后,会出现这种情况  [‘-‘, ‘-‘, ‘-‘] [‘ ‘, ‘14969037.996825399 ‘, ‘ ‘, ‘12.0/ 10.0 ‘]
 40        这需要把第2个列表中的空格都变成负号并与其后面的值拼起来,恶心死了
 41     ‘‘‘
 42     for index,i in enumerate(calc_list):
 43         if i == ‘‘: #它其实是代表负号,改成负号
 44             calc_list[index+1] = i + calc_list[index+1].strip()
 45 def handle_special_occactions(plus_and_minus_operators,multiply_and_dividend):
 46     ‘‘‘有时会出现这种情况 , [‘-‘, ‘-‘] [‘1 ‘, ‘ 2 * ‘, ‘14969036.7968254‘],2*...后面这段实际是 2*-14969036.7968254,需要特别处理下,太恶心了‘‘‘
 47     for index,i in enumerate(multiply_and_dividend):
 48         i = i.strip()
 49         if i.endswith("*") or i.endswith("/"):
 50             multiply_and_dividend[index] = multiply_and_dividend[index] + plus_and_minus_operators[index] + multiply_and_dividend[index+1]
 51             del multiply_and_dividend[index+1]
 52             del plus_and_minus_operators[index]
 53     return plus_and_minus_operators,multiply_and_dividend
 54 def compute(formula):
 55     ‘‘‘这里计算是的不带括号的公式‘‘‘
 56
 57     formula = formula.strip("()") #去除外面包的拓号
 58     formula = remove_duplicates(formula) #去除外重复的+-号
 59     plus_and_minus_operators = re.findall("[+-]", formula)
 60     multiply_and_dividend = re.split("[+-]", formula) #取出乘除公式
 61     if len(multiply_and_dividend[0].strip()) == 0:#代表这肯定是个减号
 62         multiply_and_dividend[1] = plus_and_minus_operators[0] + multiply_and_dividend[1]
 63         del multiply_and_dividend[0]
 64         del plus_and_minus_operators[0]
 65
 66     plus_and_minus_operators,multiply_and_dividend=handle_special_occactions(plus_and_minus_operators,multiply_and_dividend)
 67     for index,i in enumerate(multiply_and_dividend):
 68         if re.search("[*/]" ,i):
 69             sub_res = compute_mutiply_and_dividend(i)
 70             multiply_and_dividend[index] = sub_res
 71
 72     #开始运算+,-
 73     print(multiply_and_dividend, plus_and_minus_operators)
 74     total_res = None
 75     for index,item in enumerate(multiply_and_dividend):
 76         if total_res: #代表不是第一次循环
 77             if plus_and_minus_operators[index-1] == ‘+‘:
 78                 total_res += float(item)
 79             elif plus_and_minus_operators[index-1] == ‘-‘:
 80                 total_res -= float(item)
 81         else:
 82             total_res = float(item)
 83     print("\033[32;1m[%s]运算结果:\033[0m" %formula,total_res)
 84     return total_res
 85
 86 def calc(formula):
 87     ‘‘‘计算程序主入口, 主要逻辑是先计算拓号里的值,算出来后再算乘除,再算加减‘‘‘
 88     parenthesise_flag = True
 89     calc_res = None #初始化运算结果为None,还没开始运算呢,当然为None啦
 90     while parenthesise_flag:
 91         m = re.search("\([^()]*\)", formula) #找到最里层的拓号
 92         if m:
 93             #print("先算拓号里的值:",m.group())
 94             sub_res = compute(m.group())
 95             formula = formula.replace(m.group(),str(sub_res))
 96         else:
 97             print(‘\033[41;1m----没拓号了...---\033[0m‘)
 98
 99             print(‘\n\n\033[42;1m最终结果:\033[0m‘,compute(formula))
100             parenthesise_flag = False #代表公式里的拓号已经都被剥除啦
101
102 if __name__ == ‘__main__‘:
103
104     #res = calc("1 - 2 * ( (60-30 +(-40/5) * (9-2*5/3 + 7 /3*99/4*2998 +10 * 568/14 )) - (-4*3)/ (16-3*2) )")
105     res = calc("1 - 2 * ( (60-30 +(-9-2-5-2*3-5/3-40*4/2-3/5+6*3) * (-9-2-5-2*5/3 + 7 /3*99/4*2998 +10 * 568/14 )) - (-4*3)/ (16-3*2) )")

原文地址：https://www.cnblogs.com/zijue/p/9809851.html