bkelley at wi.mit.edu
Thu Oct 25 17:02:00 CEST 2001
David Bolen wrote:
>"Larry Whitley" <ldw at us.ibm.com> writes:
>>That's it! Here's the offending code, a little earlier in process().
>> elif pc.command == "dual": # command was a dual address cycle
>> pc.command, None, None = tr.decodeCommand()
>>Looks like it considers None a variable though it is not under the elif that
>Yes, local variable determination is a static compile-time operation,
>based on compiling an assignment, and not runtime based. But the
>error is runtime based if the variable gets used in the code path
>before being initialized.
Yeah. I got bit by this in almost my first python program. It was a
little confusing. Consider the following code:
a = [1,2,3,4,5]
len = len(a)
Traceback (most recent call last):
File "<stdin>", line 5, in ?
File "<stdin>", line 3, in bad_len
UnboundLocalError: local variable 'len' referenced before assignment
It sure teaches you not to use things like "min", "max" and "len" as
variable names really quick...
I always wanted to go into the error messages and change
UnbondLocalError for built in names to be a little more explicit about
likely errors. But once you learn what's going on then there's no need
Whitehead Institute for Biomedical Research
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