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Python Python Basics All Together Now Handle Exceptions

Roger Hauber
Roger Hauber
1,206 Points
Posted by Roger Hauber
Roger Hauber
1,206 Points

Two different ValueErrors in try block

So I'm slightly confused: in the example solution we have two different kinds of ValueError that can occur in the try block. Either a coercion ValueError because the input cannot be coerced to int() or the ValueError resulting from the tickets purchased being higher than the remaining tickets. By adding err to the print() statement in the except block, it works fine with our custom error message in the latter case, but in the coercion case it now displays the original user-unfriendly error message. How can I customize both error messages separately?

1 Answer

Megan Amendola
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STAFF
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Megan Amendola
Treehouse Teacher
Megan Amendola
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Megan Amendola
Treehouse Teacher

Hi! In the try block, the as err should print out the err message attached to the error. 

try:
    # first test
    num_tickets = int(num_tickets)
    # second test
    if num_tickets > tickets_remaining:
        raise ValueError('There are only {} tickets remaining'.format(tickets_remaining)
except ValueError as err:
    print('Oh no we ran into a problem. {}. Please try again.'.format(err))

If the first test fails, then a message like invalid literal for int() with base 10 should be added to the 'Oh no' message as the error. If the second test fails, it should add the There are only... message to 'Oh no'. Like this:

>>> How many tickets do you want? tree
Oh no we ran into a problem. invalid literal for int() with base 10: 'tree'. Please try again.
>>> How many tickets do you want? 10000
Oh no we ran into a problem. There are only 100 tickets remaining. Please try again.
Nelson Pang
Nelson Pang
2,229 Points
Nelson Pang
Nelson Pang
2,229 Points

Megan, I see how the code runs and understand your explanation - however, I think what Roger is asking and what I'm curious of also is what if when the user enters a non-number we don't want the output to say invalid literal for int() with base 10: 'tree' but INSTEAD say something more "user friendly" as is the goal like We need a number of tickets, not a word. So for example, a result that looks like this:

>>> How many tickets do you want? tree
Oh no we ran into a problem. We need a number of tickets, not a word. Please try again.
>>> How many tickets do you want? 10000
Oh no we ran into a problem. There are only 100 tickets remaining. Please try again.

I've tried fiddling around with the code to achieve this, but seem to be breaking it right now. With a little more time I think I'll get it!

EDIT: Aha! Looks like I found what I was looking for! Should've searched harder