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Python Python Basics All Together Now Handle Exceptions

"Invalid literal" when entering a character into a int question

Whenever I put a character into the "how many tickets" prompt, I get this "invalid literal". Any idea what am I doing wrong?

Script:

try: tix_purchase = int(input("Hello {}.\n How many tickets would you like? ".format(name))) if ( tix_purchase > tickets_remaining ) : raise ValueError (" We don't have {}.".format(tickets_remaining)) except ValueError as err: print ("Uh oh! Invalid entry . {} Please try again.".format(err))

Console:

Please enter your name ruben
Hello ruben.
How many tickets would you like? jk
Uh oh! Invalid entry . invalid literal for int() with base 10: 'jk' Please try again.
There are 100 tickets available

1 Answer

Asher Orr
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.a{fill-rule:evenodd;}techdegree seal-36
Asher Orr
Python Development Techdegree Graduate 9,409 Points

Hi Ruben! You are seeing that error because of this line of code:

 tix_purchase = int(input("Hello {}.\n How many tickets would you like? ".format(name))) 

Specifically this:

int

That says "Python, what my user inputs/enters is going to be an integer! Throw an error if they enter anything that isn't an integer."

Since "jk" is a string, and not an integer, Python raised that ValueError.

Does that make sense?

PS- check out the markdown cheatsheet for syntax examples on how to format your post. It will make your code easier to read!

Tricia Cruz
Tricia Cruz
915 Points

Hi Asher Orr , I came across a similar problem with the code below:

    tickets = input(f"How many tickets would you like to purchase, {first_name}? ")

    try: 
        tickets = int(tickets)
        if tickets > tickets_remaining:
            raise ValueError(f"Sorry, we don't have that many tickets left. There are only {tickets_remaining} left available.")
    except ValueError as err:
        print(f"It looks like we've come across an error. {err} Please try again.")

when I try to to give an input of "hi" (for example) when prompted "How many tickets...", I get It looks like we've come across an error. invalid literal for int() with base 10: 'hi' Please try again.

I originally had my code as

    tickets = input(f"How many tickets would you like to purchase, {first_name}? ")

    try: 
        tickets = int(tickets)
        if tickets > tickets_remaining:
            raise ValueError(f"Sorry, we don't have that many tickets left. There are only {tickets_remaining} left available.")
    except ValueError as err:
        print(err)
        print(f"It looks like we've come across an error. Please try again.")

And it came with the same issue just laid out differently so I watched the video... then we're never shown another run where a string's inputted in that prompt.

Is it really meant to come out that way? I looked back on the video and they did the same with the "tickets" variable...

edit: Oh. Okay, I think I get it. Is it because I need to do another except block, but this time for a TypeError?

edit 2: Okay that seemed to work when I did this:

    tickets = input(f"How many tickets would you like to purchase, {first_name}? ")

    try: 
        tickets = tickets
        if tickets > tickets_remaining:
            raise ValueError(f"Sorry, we don't have that many tickets left. There are only {tickets_remaining} left available.")
    except ValueError as err:
        print(err)
        print(f"It looks like we've come across an error. Please try again.")
    except TypeError:
        print("Please try again and make sure to input a whole number.") 

My question is though, is there a more concise way of doing this 😬 Unless I'm getting ahead of myself and this is going to be covered in the next video

Asher Orr
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.a{fill-rule:evenodd;}techdegree seal-36
Asher Orr
Python Development Techdegree Graduate 9,409 Points

Hi Tricia Cruz, great question.

You should check out this post on StackOverflow.

A Value error is raised when a built-in operation or function receives an argument that has the right type but an inappropriate value.

On the other hand, passing arguments of the wrong type (e.g. passing a list when an int is expected) should result in a TypeError.

  tickets = input(f"How many tickets would you like to purchase, {first_name}? ")

    try: 
        tickets = tickets
        if tickets > tickets_remaining:
            raise ValueError(f"Sorry, we don't have that many tickets left. There are only {tickets_remaining} left available.")
    except ValueError as err:
        print(err)
        print(f"It looks like we've come across an error. Please try again.")
    except TypeError:
        print("Please try again and make sure to input a whole number.") 

I put the code above into my IDE, and I got a TypeError no matter what I entered. It's because of these lines:

 try: 
        tickets = tickets
        if tickets > tickets_remaining:

The second line (in the code above) re-defines the tickets variable to be... well, whatever it was before! Since "tickets" is defined by the user's input, it will be a string (user input is always a string.)

When the script gets to the next line (if tickets > tickets_remaining), it throws this error:

TypeError: '>' not supported between instances of 'str' and 'int'

That's because tickets_remaining is an integer, but tickets is a string.

You could make your code more efficient like this:

user_selection = int(input("How many tickets would you like to buy?")
    except ValueError:
        raise ValueError("Please enter only a number.")

Remember:

A Value error is raised when a built-in operation or function receives an argument that has the right type but an inappropriate value.

When we convert the user_selection input to an integer, Python will check to see if it's the right type. It will check for a string, since user input is always a string. Then it checks for an appropriate value- a string that can be converted into an integer (like "8").

Python will consider any non-number string as an inappropriate value. Thus, it will throw a ValueError. You can simplify the error handling that way.

Does this answer your question?

Tricia Cruz
Tricia Cruz
915 Points

Yes, thank you so much!!