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Python Python Basics (2015) Number Game App Number Game Refinement

Posted by Gregory Johnson
Gregory Johnson
3,367 Points

I'm a little lost on what try and except do, it seemed like it was working with out it

What's the purpose of try and except

5 Answers

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,441 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,441 Points

The try statement allows you to run code where the outcome is uncertain. The is usually used in cases where you are dealing with results outside of you control (user input, working OS resources) or to verify the code functionality is acceptable. The except statement defines what to do in case of various errors are actually seen.

In other languages, the onus is on the programmer to protect against bad conditions explicitly, such as checking if a denominator is not zero before dividing. In python, the philosophy is "Easier to ask for forgiveness than permission" EAPF. This is contrasted to the "Look before you leap" LBYL philosophy.

Chris Freeman
Chris Freeman
Treehouse Moderator 68,441 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,441 Points

In the example of converting input to an integer instead of doing it all in one line:

try:
    guess = int(input("Guess a number between 1 and 10: "))
except ValueError:
    # some action

Use the try to capture the specific issue that it might not convert to and integer:

guess = input("Guess a number between 1 and 10: ")
try:
    guess = int(guess)
except ValueError:
    print("{} is not an integer".format(guess)
Gregory Johnson
Gregory Johnson
3,367 Points
Gregory Johnson
Gregory Johnson
3,367 Points 
guess = int(input("Guesss a number between 1 and 10"))

doesn't this statement say that only a number can be used...or was the try and except used as a way to get feedback?

[MOD: added ```python formatting -cf]

Chris Freeman
Chris Freeman
Treehouse Moderator 68,441 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,441 Points

This says "get input from user then convert to integer then a sign to the variable guess". If the user enters something that cannot be converted to an integer then a ValueError will be raised. Without a try/except statement to catch the ValueError the program will Halt

Gregory Johnson
Gregory Johnson
3,367 Points
Gregory Johnson
Gregory Johnson
3,367 Points

I see, thank you!

Benito Thompson
Benito Thompson
1,650 Points
Benito Thompson
Benito Thompson
1,650 Points

Apparently you cannot put "print(...... .format(guess))" underneath the except ValueError like you did in the video, because if you get a ValueError, it means that the guess was not assigned to the variable in the first place so it is impossible to call it. When I put print("That isn't a number!") then it worked.

I'm not sure if what I said made sense. But someone tell me if that is right or if I missed something. Thank you!

Chris Freeman
Chris Freeman
Treehouse Moderator 68,441 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,441 Points

You've got it correct! See my new comment added above.

Benito Thompson
Benito Thompson
1,650 Points
Benito Thompson
Benito Thompson
1,650 Points

Oh! I see! Thank you Chris!