0

I have a very basic assignment, but I just simply can not get the right error I am looking for. Here is the assignment:

10-6 Addition: One common problem when prompting for numerical input occurs when people provide text instead of numbers. When you try to convert the input to an int, you'll get a TypeError. Write a program that that prompts for two numbers. Add them together and print the result. Catch the TypeError if either input value is not a number, and print a friendly error message. Test your program by entering two numbers and then by entering some text instead of a number.

Here is what I have:

print("Please enter two numbers and this program will add them together!")
try:
    num_1 = int(input("What is your first number?"))
    num_2 = int(input("What is your second number?"))
    answer = num_1 + num_2
    print(str(num_1) + " + " + str(num_2) + " = " + str(answer))
except TypeError:
    print("Please make sure you enter a number next time.")

I have rearranged this for like an hour now, and no matter what I do I can't get a TypeError, only a ValueError. How am I able to get a TypeError in this, or is the book just wrong and it is impossible to get a TypeError in this scenario??

Improve this question
1
  • 1
    I thought it was a ValueError if I am not mistaken. Commented Nov 24, 2016 at 21:16

3 Answers 3

Reset to default
3 
>>> int('abc')
Traceback (most recent call last):
  File "<input>", line 1, in <module>
ValueError: invalid literal for int() with base 10: 'abc'

The book is wrong.

Improve this answer
Sign up to request clarification or add additional context in comments.

3 Comments

the book isn't wrong if it's been written when python 2 still used input. The OP wrote the code.
@Jean-FrançoisFabre Python 2's input won't raise a TypeError for any non-contrived input I can think of, and it would also make the int redundant. And it says "When you try to convert the input to an int, you'll get a TypeError".
oooooh, the book is wrong, you're right. And the example is pointless...
0

A TypeError is thrown when trying something like

answer = 2 + '3'

Your exercise is a bit misleading, because such a situation will never happen in a program like the one you are supposed to write. The error you can get when trying to explicitly convert a str to a int is a ValueError, as you say. So yes, catch the ValueError with

except ValueError:

and you are good to go.

Also, you are converting your int back into a str with the line

answer = num_1 + str(num_2)

which is incorrect. You should just do

answer = num_1 + num_2
Improve this answer

2 Comments

it happens all the time in the code above if valid numbers are entered.
It should not happen if you change your code according to the above.
0

The book is not wrong. The question didn't actually ask you to convert to int.

Just change to num_1 = input("What is your first number?") and num_2 likewise and your exception handling will be triggered if exactly one of the inputs is a string.

Granted, it's a little confusing because of the line "When you try to convert the input to int, [...]" but nowhere did it ask you to do this conversion explicitly. It was probably just referring to the implicit conversion happening when using + with an integer and a string.

To learn a little more about Python, you could also test what happens if both inputs are a string.

Improve this answer

Comments

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.