在Python中编写几行代码，创建一个基本计算器。
def add(x, y): 
   return x + y 

def subtract(x, y): 
   return x - y 

def multiply(x, y): 
   return x * y 

def divide(x, y): 
   return x / y 

num1 = float(input("输入第一个数字：")) 
num2 = float(input("输入第二个数字：")) 

print("选择操作。") 
print("1.加") 
print("2.减") 
print("3.乘") 
print("4.除") 

choice = input("输入选择(1/2/3/4):") 

if choice == '1': 
   print(num1,"+",num2,"=", add(num1,num2)) 
  
elif choice == '2': 
   print(num1,"-",num2,"=", subtract(num1,num2)) 
   
elif choice == '3': 
   print(num1,"*",num2,"=", multiply(num1,num2)) 

elif choice == '4': 
   print(num1,"/",num2,"=", divide(num1,num2)) 
else: 
   print("无效的输入")