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Patch by Tim Peters:

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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.

Example:

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

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

f()

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

D:\src\PCbuild>

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.]
This commit is contained in:
Guido van Rossum 1999-06-22 14:47:32 +00:00
parent 43128905be
commit 8746082175
4 changed files with 25 additions and 3 deletions
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4
Python/ceval.c
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@ -1320,7 +1320,7 @@ eval_code2(co, globals, locals,
case LOAD_FAST:
x = GETLOCAL(oparg);
if (x == NULL) {
PyErr_SetObject(PyExc_NameError,
PyErr_SetObject(PyExc_UnboundLocalError,
PyTuple_GetItem(co->co_varnames,
oparg));
break;
@ -1338,7 +1338,7 @@ eval_code2(co, globals, locals,
case DELETE_FAST:
x = GETLOCAL(oparg);
if (x == NULL) {
PyErr_SetObject(PyExc_NameError,
PyErr_SetObject(PyExc_UnboundLocalError,
PyTuple_GetItem(co->co_varnames,
oparg));
break;