Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

Python Python Basics Functions and Looping Raising Exceptions

Posted by Aassem Hadiouche
Aassem Hadiouche
6,570 Points

Question about logic of "as err"

When Craig is explaining how to get the ValueError message from the function, he says to change the "except ValueError:" code to "except ValueError as err:" and then he also needs to print a message with ".format(err)" to get the original message from the function.

It's not clicking for me how python knows to refer to the "raise ValueError" in the function when you are in the try block of code.

Do you have to use the keyword "err" in this case?

What does "as" do so that the compiler knows to refer back the "raise ValueError" in the function?

I imagine there's some detail I'm forgetting that puts all the pieces together but it's not coming to me. Thanks in advance for any and all help!

2 Answers

Steven Parker
Steven Parker
231,236 Points
Steven Parker
Steven Parker
231,236 Points

The "except" by itself responds to the ValueError.

What the "as" does is save the error object where you can get to it in the handler code. The term after "as" is the name of the variable where you want it to be saved (in this case, "err").

Zahkyi Ferguson
Zahkyi Ferguson
504 Points

Thank you for your explanation. So "as" essentially creates variables for error objects, what kind of value is "as"?

Steven Parker
Steven Parker
231,236 Points
Steven Parker
Steven Parker
231,236 Points

It's an operational keyword, like "except".

ChiaChi Chang
ChiaChi Chang
273 Points
ChiaChi Chang
ChiaChi Chang
273 Points

understood about the "as" is creating a variables

but how compiler knows the variable after "as" ("err" in this case) refer back the "raise ValueError" in the function? I thought it could be showed the result of "except" again

Steven Parker
Steven Parker
231,236 Points
Steven Parker
Steven Parker
231,236 Points

The systems puts an object containing data about the exception into the variable when the exception happens. In this case, it is caused by the "raise" statement.