Python 计算器开发

Posted 2020-12-05 搬砖创造世界

计算器开发

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，结果必须与真实的计算器所得出的结果一致

  1 import re
  2 #检查表达式合法性
  3 def check_expression(string):
  4     check_result = True
  5     #括号是否匹配
  6     if not string.count("(") == string.count(")"):
  7         print("表达式错误，括号未闭合！")
  8         check_result = False
  9     if re.findall(‘[a-z]‘,string.lower()):
 10         print("表达式错误，包含非法字符！")
 11         check_result = False
 12 
 13     return check_result
 14 
 15 #格式化字符串
 16 def format_string(string):
 17     string = string.replace("--","+")
 18     string = string.replace("-+","-")
 19     string = string.replace("++","+")
 20     string = string.replace("+-","-")
 21     string = string.replace("*+","*")
 22     string = string.replace("/+","/")
 23     string = string.replace(‘ ‘,‘‘)
 24     return string
 25 
 26 #计算乘，除法#(30+6*2)
 27 def calc_mul_div(string):
 28     #从字符串中获取一个乘法的表达式
 29     # regular = "d+.{0,}d{0,}[*/][-]{0,}d+.{0,}d{0,}"
 30     regular = "d+.?d*([*/]|**)[-]?d+.?d*"
 31     #如果还能找到乘或除法表达式
 32     while re.findall(regular,string):
 33         #获取表达式
 34         expression = re.search(regular,string).group()
 35 
 36         #如果是乘法
 37         if expression.count("*")==1:
 38             #获取要计算的两个数
 39             x,y = expression.split("*")
 40             #计算结果
 41             mul_result = str(float(x) * float(y))
 42             #将计算的表达式替换为计算结果值
 43             string = string.replace(expression,mul_result)
 44             #格式化一下
 45             string = format_string(string)
 46 
 47         #如果是除法
 48         if expression.count("/"):
 49             #获取要计算的两个数
 50             x,y = expression.split("/")
 51             #计算除法
 52             div_result = str(float(x) / float(y))
 53             #用结果替换表达式
 54             string = string.replace(expression,div_result)
 55             string = format_string(string)
 56 
 57         if expression.count(‘*‘)==2:
 58             x,y = expression.split(‘**‘)
 59             pow_result = 1
 60             for i in range(int(y)):
 61                 pow_result*=int(x)
 62             string = string.replace(expression,str(pow_result))
 63             string = format_string(string)
 64     return string
 65 
 66 #计算加，减法
 67 def calc_add_sub(string):##(30+12-23+24-3)
 68     #(30+12-23+24-3)
 69     #定义正则表达式
 70     #add_regular = "[-]{0,}d+.{0,}d{0,}+[-]{0,}d+.{0,}d{0,}"
 71     #sub_regular = "[-]{0,}d+.{0,}d{0,}-[-]{0,}d+.{0,}d{0,}"
 72     add_regular = ‘[-]?d+.?d*+[-]?d+.?d*‘
 73     sub_regular = ‘[-]?d+.?d*-[-]?d+.?d*‘
 74 
 75     #开始加法
 76     while re.findall(add_regular,string):
 77         #把所有的加法都算完，获取所有加法表达式
 78         add_list = re.findall(add_regular,string)
 79         for add_str in add_list:
 80             #获取两个加法的数
 81             x,y = add_str.split("+")
 82             add_result = "+" + str(float(x) + float(y))
 83             string = string.replace(add_str,add_result)
 84         string = format_string(string)
 85 
 86     #开始减法
 87     while re.findall(sub_regular,string):
 88         sub_list = re.findall(sub_regular,string)
 89         for sub_str in sub_list:
 90             numbers = sub_str.split("-")
 91             #-3-5的情况split会返回3个值
 92             if len(numbers) == 3:
 93                 result = 0
 94                 for v in numbers:
 95                     if v:
 96                         result -= float(v)
 97             else:
 98                 x,y = numbers
 99                 result = float(x) - float(y)
100             #替换字符串
101             string = string.replace(sub_str,"+" + str(result))
102         string = format_string(string)
103     return string
104 
105 
106 
107 
108 if __name__ == "__main__":
109     source = ‘1 - 2 * ( (60-30 +(-40/5) * (9-2*5/3 + 7 /3*99/4*2998 +10 * 568/14 )) - (-4*3)/ (16-3*2) )‘
110     #source = "2-((-40/5)*(4-3))"
111     #source = "3**2"
112     #source = "3*6*8"
113 
114     if check_expression(source):
115         print("source:",source)
116         print("eval result",eval(source))
117         source = format_string(source)
118         print(source)
119 
120         while source.count("(") > 0:
121             #格式化
122             #去括号，得到括号的字符串，结果如：(30+6/3)
123             strs = re.search(‘([^()]*)‘,source).group()
124             #将括号的表达式进行乘，除运算
125             replace_str = calc_mul_div(strs)
126             #将运算的结果在进行加，减运算
127             replace_str = calc_add_sub(replace_str)
128             #将括号的字符串替换为计算结果，结果包含()，替换时去掉():[1:-1]
129             source = format_string(source.replace(strs,replace_str[1:-1]))
130 
131         else:
132             #没有括号就到最后单一表达式了
133             # 算乘除
134             replace_str = calc_mul_div(source)
135             #算加减
136             replace_str = calc_add_sub(replace_str)
137             source = source.replace(source,replace_str)
138         print("my result:",source.replace("+",""))

1 source: 1 - 2 * ( (60-30 +(-40/5) * (9-2*5/3 + 7 /3*99/4*2998 +10 * 568/14 )) - (-4*3)/ (16-3*2) )
2 eval result 2776672.6952380957
3 1-2*((60-30+(-40/5)*(9-2*5/3+7/3*99/4*2998+10*568/14))-(-4*3)/(16-3*2))
4 my result: 2776672.6952380957
5 
6 Process finished with exit code 0