[Python-checkins] CVS: python/dist/src/Python bltinmodule.c ceval.c

Guido van Rossum guido@cnri.reston.va.us
Tue, 22 Jun 1999 10:47:33 -0400 (EDT)

Update of /projects/cvsroot/python/dist/src/Python
In directory eric:/projects/python/develop/guido/src/Python

Modified Files:
	bltinmodule.c ceval.c 
Log Message:
Patch by Tim Peters:

Introduce a new builtin exception, UnboundLocalError, raised when ceval.c
tries to retrieve or delete a local name that isn't bound to a value.
Currently raises NameError, which makes this behavior a FAQ since the same
error is raised for "missing" global names too:  when the user has a global
of the same name as the unbound local, NameError makes no sense to them.
Even in the absence of shadowing, knowing whether a bogus name is local or
global is a real aid to quick understanding.


D:\src\PCbuild>type local.py
x = 42

def f():
    print x
    x = 13
    return x


D:\src\PCbuild>python local.py
Traceback (innermost last):
  File "local.py", line 8, in ?
  File "local.py", line 4, in f
    print x
UnboundLocalError: x


Note that UnboundLocalError is a subclass of NameError, for compatibility
with existing class-exception code that may be trying to catch this as a
NameError.  Unfortunately, I see no way to make this wholly compatible
with -X (see comments in bltinmodule.c):  under -X, [UnboundLocalError
is an alias for NameError --GvR].

[The ceval.c patch differs slightly from the second version that Tim
submitted; I decided not to raise UnboundLocalError for DELETE_NAME,
only for DELETE_LOCAL.  DELETE_NAME is only generated at the module
level, and since at that level a NameError is raised for referencing
an undefined name, it should also be raised for deleting one.]