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Python Python Basics All Together Now Handle Exceptions

Isaiah Dicristoforo
Isaiah Dicristoforo
1,135 Points
Posted by Isaiah Dicristoforo
Isaiah Dicristoforo
1,135 Points

How do we print out separate error messages for each exception?

In the video, we have a single except block to catch both value errors. If the user does not enter a number, our except block prints a confusing message. If we enter a ticket number greater than the total tickets available, we raise an exception and print out a custom error message. How would we catch each ValueError separately, and print out a descriptive message for each?

5 Answers

Steven Parker
Steven Parker
231,275 Points
Steven Parker
Steven Parker
231,275 Points

One idea is to detect the system messages by their content, and issue a custom replacement. For example:

    except ValueError as err:
        if "invalid literal for int" in err:  # substitute this confusing message
            print("Sorry, but you must enter a number!")
        else:                                 # otherwise print what we got
            print(err)
Isaiah Dicristoforo
Isaiah Dicristoforo
1,135 Points
Isaiah Dicristoforo
Isaiah Dicristoforo
1,135 Points

Thanks for your help! I like your approach.

Steven Parker
Steven Parker
231,275 Points
Steven Parker
Steven Parker
231,275 Points

The "as" variable is an exception object, which contains the string you passed in. It has a "__str__" override that will return that string if the object is accessed as a string.

Bruno Correia
Bruno Correia
3,114 Points
Bruno Correia
Bruno Correia
3,114 Points

Steven Parker I tried that but ran into a different TypeError that says that ValueError is not iterable. After checking online I could fix it by changing the code to 

if "invalid literal for int" in str(err):

but now I'm confused. Isn't err a string already since it's passed the text that comes from ValueError?

If it helps, this is what I got at first when not using str(err)

Traceback (most recent call last):
  File "masterticket.py", line 12, in <module>
    num_tickets = int(num_tickets)
ValueError: invalid literal for int() with base 10: 'blue'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "masterticket.py", line 17, in <module>
    if "invalid literal for int" in err:
TypeError: argument of type 'ValueError' is not iterable
Bruno Correia
Bruno Correia
3,114 Points
Bruno Correia
Bruno Correia
3,114 Points

That's great, thank you!

jaime munoz
jaime munoz
1,438 Points
jaime munoz
jaime munoz
1,438 Points

Great solution thanks!