On Jan 22, 8:39 pm, Martin Drautzburg <martin.drautzb...@web.de>
wrote:
> Martin Drautzburg wrote:
> >> with scope():
> >> # ...
> >> # use up, down, left, right here
>
> >> # up, down, left, right no longer defined after the with block exits.
>
> Just looked it up again. It's a cool thing. Too bad my locals() hack
> would still be required. The result would be less noisy (and actually
> really beautiful) than the decorator implementation though. Thanks
> again for pointing this out to me.
Both in your example and by using a context manager, you can get away
with not passing locals() explicitly by introspecting the stack frame.
Here's a context manager that does the trick:
from __future__ import with_statement
from contextlib import contextmanager
import sys
@contextmanager
def enums(*consts):
# 2 levels up the stack to bypass the contextmanager frame
f_locals = sys._getframe(2).f_locals
new_names = set()
reset_locals, updated_locals = {}, {}
for const in consts:
updated_locals[const] = const
if const in f_locals:
reset_locals[const] = f_locals[const]
else:
new_names.add(const)
f_locals.update(updated_locals)
try:
yield
finally:
for name in new_names:
del f_locals[name]
f_locals.update(reset_locals)
if __name__ == '__main__':
def move(aDirection):
print "moving " + aDirection
up = "outerScopeUp"
with enums("up", "down", "left", "right"):
move(up)
move(down)
move(left)
move(right)
print "in the outer scope up is still:", up
print "this should fail:"
down
Of course, as all other attempts to mess with locals() shown in this
thread, this only "works" when locals() is globals(). If you try it
within a function, it fails:
def test():
up = "outerScopeUp"
with enums("up", "down", "left", "right"):
move(up)
move(down)
move(left)
move(right)
print "in the outer scope up is still:", up
print "this should fail:"
down
## XXX: doesn't work within a function
test()
So it's utility is pretty limited; a custom DSL is probably better
suited to your problem.
George
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