Le 3 janv. 2018 06:34, "Guido van Rossum" <gu...@python.org> a écrit :
I think the issue here is a bit different than Yury's response suggests --
it's more like how a variable containing an immutable value (e.g. a string)
can be modified, e.g.
x = 'a'
x += 'b'
In our case the *variable* is the current thread state (in particular the
slot therein that holds the context -- this slot can be modified by the C
API). The *value* is the Context object. It is a collections.Mapping (or
typing.Mapping) which does not have mutating methods. (The mutable type is
called MutableMapping.)
I can see a parallel with a Python namespace, like globals and locals
arguments of exec():
ns = globals().copy() # ctx = copy_context()
exec("x = 'a'", ns, ns) # ctx.run(...)
ns['x'] += 'b' # Context ???
print(ns ['x']) # print(ctx[x])
The *reason* for doing it this way is that Yury doesn't want Context to
implement __delitem__, since it would complicate the specification of
chained lookups by a future PEP, and chained lookups look to be the best
option to extend the Context machinery for generators.
Again, why not just raise an exception on "del ctx[var]"?
Victor
_______________________________________________
Python-Dev mailing list
Python-Dev@python.org
https://mail.python.org/mailman/listinfo/python-dev
Unsubscribe:
https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
