I teach a computing subject to high school students using Python as our primary language. One thing that often causes confusion at the start is error messages/exceptions. I think it would lower entry point quite a bit by making error messages more readable to novices. Recent research found reduced frequency of overall errors, errors per student, and repeated errors when error messages were enhanced [1].


This could be implemented by a command-line switch when running python, or a different python executable (along the lines of pythonw.exe vs python.exe) such as python-easy. A simpler error message might get rid of excess information which can confuse the novice (such info might be dumped to a file to allow more advanced users to debug), provide a brief description of what the error might mean, and/or how you might fix it. So a SyntaxError might tell the user that they've probably forgotten a :, and a NameError might say that the item has been defined yet, or they've made a typo. A couple of examples follow:


Traceback (most recent call last):

 File "foo.py", line 2, in <module>

   l[10]=14

IndexError: list assignment index out of range


A better message might be:

You tried to use l[10] when l is only 4 elements long. You can add items to l using l.append(value), or check your index value to make sure that's really the position you wanted to access.


Traceback (most recent call last):

 File "foo.py", line 2, in <module>

   while name != "quit" and reponse != "quit":

NameError: name 'reponse' is not defined

A better message might be:

You're trying to use the value of 'reponse', but that variable hasn't got a value yet. You can give it a value earlier in the code, or it could be a typo. You have a variable called 'response' - is that the one you meant?


Traceback (most recent call last):

 File "foo.py", line 2, in <module>

   print(length(l))

NameError: name 'length' is not defined

A better message might be:

Python doesn't recognise the function "length". Did you mean len?'


 File "foo.py", line 2

   for i in l

            ^

SyntaxError: invalid syntax

A better message might be:

You have a for loop without a : (colon). Try adding a colon at the end of the line.



Any thoughts?

[1]: http://researchrepository.ucd.ie/handle/10197/7583
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Victor Rajewski