python - 简化代码-根据运算符执行数学运算

Question

这是Python中计算器的代码:

import time
#Returns the sum of num1 and num2
def add(num1, num2):
    return num1 + num2

#Returns the difference of num1 and num2
def subtract(num1, num2):
    return num1 - num2

#Returns the quotient of num1 and num2
def divide(num1, num2):
    return num1 / num2

#Returns the product of num1 and num2
def multiply(num1, num2):
    return num1 * num2

#Returns the exponentiation of num1 and num2
def power(num1, num2):
    return num1 ** num2

import time

def main ():
    operation = input("What do you want to do? (+, -, *, /, ^): ")
    if(operation != "+" and operation != "-" and operation != "*" and operation != "/" and operation != "^"):
        #invalid operation
        print("You must enter a valid operation")
        time.sleep(3)
    else:
        var1 = int(input("Enter num1: ")) #variable one is identified
        var2 = int(input("Enter num2: ")) #variable two is identified
        if(operation == "+"):
            print (add(var1, var2))
        elif(operation == "-"): 
            print (subtract(var1, var2))
        elif(operation == "/"): 
            print (divide(var1, var2))
        elif(operation == "*"):
            print (multiply(var1, var2))
        else:
            print (power(var1, var2))
main()
input("Press enter to exit")
exit()

大约30分钟前，我找到了旧的Python文件夹，并查看了8个月前的所有基本脚本。我找到了我的计算器迷你脚本，并认为以最少的行数重新创建它会很有趣(我现在正在学习lambda)。这是我所拥有的:

main = lambda operation,var1,var2: var1+var2 if operation=='+' else var1-var2 if operation=='-' else var1*var2 if operation=='*' else var1/var2 if operation=='/' else 'None'
print(main(input('What operation would you like to perform? [+,-,*,/]: '),int(input('Enter num1: ')),int(input('Enter num2: '))))
input('Press enter to exit')

我知道这是根据我的具体情况提出的一个个人问题，但我希望能将其缩短为任何帮助。有没有办法使它更Pythonic？我是否正确使用lambda？有没有办法处理我的简化版本中的错误？任何帮助，将不胜感激。我对此很陌生。谢谢!

Answer 1

为了简化代码，我建议:

创建一个函数以借助字典进行操作。

注意:根据用户提到的要求，我使用lambda函数来替代方法。我个人将使用 operator

使用operator:

import operator

def perform_operation(my_operator):
    return {
        '+': operator.add,
        '-': operator.sub,
        '*': operator.mul,
        '/': operator.truediv,  # "operator.div" in python 2
        '^': operator.pow,
   }.get(my_operator, '^')  # using `^` as defualt value since in your 
                            # "else" block you are calculating the `pow` 

使用lambda:

def perform_operation(my_operator):
    return {
        '+': lambda x, y: x + y,
        '-': lambda x, y: x - y,
        '*': lambda x, y: x * y,
        '/': lambda x, y: x / float(y), 
        '^': lambda x, y: x ** y,
   }.get(my_operator, '^')  # using `^` as defualt value since in your 
                            # "else" block you are calculating the `pow()`

sample 运行:

>>> perform_operation('/')(3, 5)
0.6

PS:看一下定义，您会知道为什么使用operator比lambda更加pythonic

更新您的else块以使其调用为:

var1 = int(input("Enter num1: ")) 
var2 = int(input("Enter num2: ")) 
perform_operation(operation)(var1, var2)  # Making call to function created above
# THE END - nothing more in else block

使用以下方法简化if的条件:

if operation not in ["+", "-", "*", "/", "^"]:
    # invalid operation