Python comparison operator not giving proper answer in if-else statements

Question

# Program1: Take two numbers as input from User and print which one is greater or are they equal.

num1 = input("Enter the first number: ")
num2 = input("Enter the second number: ")
if num1 is num2:
    print("The two numbers are equal")
elif num1 < num2:
    print("The first number is less than the second number")
else:
    print("The first number is greater than the second number")

Enter the first number: -10 Enter the second number: -20 The first number is less than the second number

Process finished with exit code 0

What is wrong in above code to compare two numbers? How come python missing basic -ve number comparison?

Does this answer your question? When, if ever, to use the 'is' keyword in Python? — Gaberocksall
– Gaberocksall, Commented Feb 21, 2024 at 9:30
Also, your inputs are string values - comparing them like num1 < num2 compares the strings lexicographically (basically, alphabetically). If you want to compare them numerically, you'll need to parse those strings into numbers. — Gaberocksall
– Gaberocksall, Commented Feb 21, 2024 at 9:31

Raky · Accepted Answer · 2024-02-21 09:41:38Z

First, input() returns string. SO you need to cast the input values to integer by using int().

Second, when you use if num1 is num2:, the is operator(keyword) is testing if num1and num2refer to the same object or not.

Third, Enter the first number: -10 Enter the second number: -20 The first number is less than the second number

Process finished with exit code 0

You know that -10 and -20 are numbers, but as mentioned in First Para above, input()is returning string values, python is doing lexicographical comparison, and ascii of - is highter than digit.

So, your code should be like this instead

num1 = int(input("Enter the first number: "))
num2 = int(input("Enter the second number: "))

if num1 == num2:
    print("The two numbers are equal")
elif num1 < num2:
    print("The first number is less than the second number")
else:
    print("The first number is greater than the second number")

tho · Accepted Answer · 2024-02-21 09:33:39Z

0

In your case you should use '==' statement instead of 'is' statement.

'==' actually compare the value where 'is' check if they are same object.

See a previous discussion about that

answered Feb 21, 2024 at 9:33

tho

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2 Comments

Sergio García Over a year ago

Since what he tries to do is to not only check if they are the same value but also to check what value is higher/lower the best way to do it is to parse the inputs to int values and then do those comparisons instead of just using the '==' statement.

Sergio García Over a year ago

Since what he tries to do is to not only check if they are the same value but also to check what value is higher/lower the best way to do it is to parse the inputs to int values and then do those comparisons instead of just using the '==' statement.

Ada · Accepted Answer · 2024-02-21 09:34:26Z

0

You are doing a string comparison, not a numerical comparison. The string "-10" does come before "-20" since "1" comes before "2" in lexicographical order. To do an integer comparison you should cast the values you receive to int:

num1 = int(input("Enter the first number: "))
num2 = int(input("Enter the second number: "))

answered Feb 21, 2024 at 9:34

Ada

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