Issue 6833: incorrect: failed local variable referenced before assignment

The attached python file will give the following output, which is 
incorrect behavior as far as I know:
"
this will fail
failed local variable 'in_std' referenced before assignment

this won't fail
Not failed
this won't fail either
Not failed
"

This is tested on windows with python2.6(standard msi) and on centos 
5.3 with python2.6 (custom rpm), python2.4 (system rpm), freebsd with 
python2.5 (system package), python2.6 ("hand" compiled) and python3.0 
("hand" compiled).

The attached code is stripped down to the bare minimum and therefore 
won't do anything usefull.

This is not a bug.  The behaviour you're seeing is described here:

http://docs.python.org/reference/executionmodel.html#naming-and-binding

"If a name binding operation occurs anywhere within a code block, all
uses of the name within the block are treated as references to the
current block. This can lead to errors when a name is used within a
block before it is bound. This rule is subtle. Python lacks declarations
and allows name binding operations to occur anywhere within a code
block. The local variables of a code block can be determined by scanning
the entire text of the block for name binding operations."

In the failing example, the registerdecorator function contains an
assignment to in_std, so by the rules above in_std is local to the
function.  The 'if in_std' line therefore tries to lookup 'in_std' in
the local namespace;  it doesn't exist (yet), so an UnboundLocalError
exception occurs.

nosy: + mark.dickinson
messages: + msg92201

resolution: not a bug