用python寫一個計算器

一個簡單的計算器，能計算括號加減乘除，由於還沒有加入判斷輸入規范的功能，所以格式必須正確
例如：3/3*(25-6/3)+(1+4)/2.5
ps：不能用python自帶的eval或者exec等方法
有兩個方案，方案一是早期寫的，能夠實現，但代碼較亂，方案二比較簡潔易懂些，在頁面看，可能代碼看起來會是亂的，復制到編輯器就不會了
方案一
#Auther:He Jianhan
import re

def mul_div(front,after,symbol):
    #計算帶入的值進行計算*和/
    if symbol == "*":
        result = float(front) * float(after)
    else:
        result = float(front) / float(after)
    return result

def add_sub(front,after,symbol):
    # 計算帶入的值進行計算+和-
    if symbol == "+":
        result = float(front) + float(after)
    else:
        result = float(front) - float(after)
    return result

def process(value,one,two,functions,itmes):
    #通過判斷列表是否有四則運算，調取加減乘除的運算函數，不斷進行計算
    for symbol_list_number,symbol_list_forin in enumerate(value):
        if one in symbol_list_forin:
            result = functions(itmes[symbol_list_number],itmes[symbol_list_number+1], one)
            itmes[symbol_list_number] = str(result)
            itmes[symbol_list_number+1] = str(result)
        elif two in symbol_list_forin:
            result = functions(itmes[symbol_list_number], itmes[symbol_list_number+1], two)
            itmes[symbol_list_number] = str(result)
            itmes[symbol_list_number+1] = str(result)

def main(number):
    digit_list = []
    symbol_list = []
    number_list = re.findall("^[0-9]+|..[0-9]+[.][0-9]+|..[0-9]+|.[0-9]+[.][0-9]+|"
                             ".[0-9]+",number)#將要計算的數值進行分開
    for n in number_list:
        #將加減乘除和數值分開，以便於后面計算
        if "*" in n or "/" in n or "+" in n or "-" in n:
            digit_list.append(n[1:])
            symbol_list.append(n[0])
        else:
            digit_list.append(n[:])
    if "-" in number_list[0]:
        #判斷第一個輸入的值是否為負數，是負數則將dict_list列表的第一個值進行替換
        # 並刪除symbol_list的第一個符號
        digit_list[0] = number_list[0]
        del symbol_list[0]

    process(symbol_list,"*","/",mul_div,digit_list)


    while  "*" in symbol_list or "/" in symbol_list:
        #將已經計算過才*和/進行刪除
        if "*" in symbol_list:
            del digit_list[symbol_list.index("*")]
            symbol_list.remove("*")
        if "/" in symbol_list:
            del digit_list[symbol_list.index("/")]
            symbol_list.remove("/")
    process(symbol_list,"+","-",add_sub,digit_list)
    return digit_list[-1]


number = input("輸入你要計算的\033[31;1m公式\033[0m")

while True:
    #判斷是否有括號，有括號則先進行括號內的運算
    if "(" in number:
        left = number.find(")")
        right = number[:left].rfind("(")
        number_small = number[right+1:left]
        replace = main(number_small)
        number = number[:right] + replace + number[left+1:]
    else:
        print("===>"+main(number))
        break
方案二

import re
def count1(number):
   # 利用正則匹配出乘除，計算，並不斷循環直到沒有乘除，並計算返回結果
   while True:
      search_var = re.search("[+\-/*]?-?\d+(\.\d+)?([/*])-?\d+(\.\d+)?",number)
      if not search_var:
         break
      if  search_var.group()[0] not in ["+","-","/","*"]:
         var = search_var.group()
      else:
         var = search_var.group()[1:]
      if "*" in var:
         a,b = var.split("*")
         var = str(float(a)*float(b))
      else:
         a, b = var.split("/")
         var = str(float(a) / float(b))
      if  search_var.group()[0] not in ["+", "-", "/", "*"]:
         number = number[:search_var.span()[0]] + var + number[search_var.span()[1]:]
      else:
         number = number[:search_var.span()[0]+1]+var+number[search_var.span()[1]:]
   return str(number)



def count2(number):
   # 利用正則匹配出加減，計算，並不斷循環直到沒有加減，並計算返回結果
   while True:
      search_var =re.search("-?\d+(\.\d+)?([+-])-?\d+(\.\d+)?",number)
      if not search_var:
         break
      var = search_var.group()
      if "+" in var:
         a,b = var.split("+")
         var = str(float(a) + float(b))
      else:
         if var[0] == "-":
            new_var = var[1:]
            find_var = new_var.find("-")
            a = new_var[:find_var]
            b = new_var[find_var+1:]
            a = "-" + a
         else:
            find_var = var.find("-")
            a = var[:find_var]
            b = var[find_var + 1:]
         var = str(float(a) - float(b))
      number = number[:search_var.span()[0]]+var+number[search_var.span()[1]:]
   return str(number)



def bracket(number):
   # 匹配出里層括號
   search_var = re.search("\([\d+\-/*.]*[^(][\d+\-/*.]*\)",number)
   return search_var



if __name__ == "__main__":
   while True:
      number = input("請輸入要計算的公式，小數負數隨便輸，算錯算我輸(q/Q退出)")
      if number.upper() == "Q":
         print(1)
         break
      else:
         while True:
            search_var = bracket(number)
            if not search_var:
               break
            count_var = count1(search_var.group()[1:-1])
            count_var = count2(count_var)
            number = number[:search_var.span()[0]] + count_var + number[search_var.span()[1]:]
         number = count1(number)
         number = count2(number)
      print(number)