Matthias Bussonnier added the comment:
> Wouldn't be better to say just "local variable 'xxx' is not set"?
Thank you for responding that fast and for your interest in this issue.
While I think that "local variable 'xxx' is not set" is technically correct, I
think it would be a step back.
The improvement of the error message is not really meant for the 99% of the
developers hanging on b.p.o. I think for these just the fact that there is an
UnboundLocalError is sufficient to know what's happening.
The error message will mostly be useful for users that still don't have much
clue about what's going on. For these kind of users UnboundLocalError("local
variable 'xxx' is not set") is not much different from NameError("name 'xxx' is
not defined")[*]
The current error message already does a good job at giving some extra hint as
to why this is the case. In particular that it is (often) assigned but not in
the right place. Changing to "local variable 'xxx' is not set" will likely make
many novices check the spelling, and be more confused.
Note that "local variable 'xxx' referenced before assignment, or got deleted"
would not be completely obvious for novices either, why would the following not
trigger such an error ?
In [1]: def foo():
...: if False:
...: print(n)
...: n = 1
Well, for you and me it's (likely) obvious.
I want to point out (just stealing rhettinger example) that it might not be
obvious either the variable has been deleted:
In [5]: def foo():
...: n = 1
...: def g(): # imagine a more complex g
...: del n
...: g()
...: print(n) #UnboundLocalError
...:
So I think expanding the error message to give hints as of _why_ is better than
just stating what is.
[*] Source: The users I work with. Last question I got on wednesday: "Can you
re-explain the difference between a string and a function". They meant "list"
and "list comprehension".
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue29593>
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