[Python-Dev] PEP 567 v2 (original) (raw)

Guido van Rossum guido at python.org
Wed Jan 3 17:01:49 EST 2018

On Wed, Jan 3, 2018 at 12:32 PM, Glenn Linderman <v+python at g.nevcal.com> wrote:

On 1/3/2018 11:16 AM, Guido van Rossum wrote:

Maybe I should clarify again what run() does. Here's how I think of it in pseudo code: def run(self, func, *args, **kwds): old = getcurrentcontext() new = old.copy() setcurrentcontext(new) try: return func(*args, **kwds) finally: setcurrentcontext(old) I find it interesting that self isn't used in the above pseudo-code. I thought that Context.run() would run the function in the "context" of self, not in the context of a copy of "current context".

Heh, you're right, I forgot about that. It should be more like this:

def run(self, func, *args, **kwds): old = _get_current_context() _set_current_context(self) # <--- changed line try: return func(*args, **kwds) finally: _set_current_context(old)

This version, like the PEP, assumes that the Context object is truly immutable (not just in name) and that you should call it like this:

contextvars.copy_context().run(func, )

The PEP definitely needs to be clearer about this -- right now one has to skip back and forth between the specification and the implementation (and sometimes the introduction) to figure out how things really work. Help is wanted!

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