Entry

What is UnboundLocalError for?

Jul 13th, 2000 18:42
unknown unknown, Tim Peters

When a local name is referenced but has not been bound to a value.  In 
other words, it's an unbound local error <wink>.  Note that 
UnboundLocalError is a subclass of NameError, because it's a more 
specific form of NameError, so old code expecting to catch NameError 
exceptions will still catch UnboundLocalError exceptions.  In 1.5.2 and 
before, NameError was thrown regardless of whether the offending name 
was local or global.  So UnboundLocalError gives more information.
> I encountered it when I made a mistake like this:
>
> >>> f()
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
>   File "<stdin>", line 1, in f
> UnboundLocalError: l
> >>>
So your function f (which you have not shown us) refers to a local name 
"l" which you didn't give a value before referencing it.  It's 
impossible for us to guess what you put in the body of f; here's one 
possibility:
>>> def f():
...     l = l + 1   # local "l" referenced on the right before 
definition
...     return l
...
>>> f()
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "<stdin>", line 2, in f
UnboundLocalError: l
>>>