repeating input

Question

I want to program it like that so while taking input of num1,num2 and operation if user doesn't give input in appropriate type it ask the user again for input.

operation=(input('1.add\n2.subtract\n3.multiply\n4.divide'))
num1 =int(input("Enter first number: "))
num2 = int(input("Enter second number: "))
if operation == "add" or operation == '1' :
 print(num1,"+",num2,"=", (num1+num2))
elif operation =="subtract" or operation == '2':
 print(num1,"-",num2,"=", (num1-num2))
elif operation =="multiply" or operation == '3':
 print(num1,"*",num2,"=", (num1*num2))
elif operation =="divide" or operation == '4':
 print(num1,"/",num2,"=", (num1/num2))

• Sayse: Possible duplicate of How to test multiple variables against a value?
• molbdnilo: Start your Python, enter "2" == "1" or "add" and consider the result.

Answer 1

Try this,

 operation=(input('1.add\n2.subtract\n3.multiply\n4.divide'))
 num1 = int(input("Enter first number: "))
 num2 = int(input("Enter second number: "))
 if operation == "1" or operation == "add" :
 print(num1,"+",num2,"=", (num1+num2))
 elif operation == "2" or operation == "subtract":
 print(num1,"-",num2,"=", (num1-num2))
 elif operation == "3" or operation == "multiply":
 print(num1,"*",num2,"=", (num1*num2))
 elif operation == "4" or operation == "divide":
 print(num1,"/",num2,"=", (num1/num2))
 else:
 print("Invalid Input")

Explanation:

In your code, IF will check condition-1 or condition-2 are True or False

if operation == "1" or operation == "add" 

here,

condition-1: operation == "1"

condition-2: operation == "add"

if operation == "1" or operation == "add" 

here,

condition-1: operation == "1"

condition-2: "add" # Always True as string contains elements.

• Harsha Biyani: it is better to use operation in ["1","add"] rather than operation == "1" or operation == "add" .

Answer 2

You can use in keyword.

Ex:

>>> "1" in ["1","add"]
True
>>> "add" in ["1","add"]
True

Modify code like:

 operation=(input('1.add\n2.subtract\n3.multiply\n4.divide'))
 num1 = int(input("Enter first number: "))
 num2 = int(input("Enter second number: "))
 if operation in ["1","add"] :
 print(num1,"+",num2,"=", (num1+num2))
 elif operationi in ["2", "subtract"]:
 print(num1,"-",num2,"=", (num1-num2))
 elif operation in ["3", "multiply"]:
 print(num1,"*",num2,"=", (num1*num2))
 elif operation in ["4", "divide"]:
 print(num1,"/",num2,"=", (num1/num2))
 else:
 print("Invalid Input")

Answer 3

This code is valid because in Python values are either truthy and falsy. However, the syntax for multicondition if clause is wrong. It should be if a == something and b == anotherthing.

So it will be as follows.

if operation == "1" or operation == "add" :
 print(num1,"+",num2,"=", (num1+num2))

• Harsha Biyani: it is better to use operation in ["1","add"] rather than operation == "1" or operation == "add" .
• Mansur: I know, however, the requester didn't ask for it. He said he cannot use 2 statements, that's why I mentioned this way. Nevertheless, you're absolutely right.