On Tue, Oct 10, 2017 at 3:42 PM, Nick Coghlan <ncoghlan@gmail.com> wrote:
On 10 October 2017 at 22:34, Koos Zevenhoven <k7hoven@gmail.com> wrote:
Really, it was my mistake to ever make you think that context_var.assign(42).__enter__() can be compared to .set(42) in PEP 550. I'll say it once more: PEP 555 context arguments have no equivalent of the PEP-550 .set(..).

Then your alternate PEP can't work, since it won't be useful to extension modules.


​Maybe this helps:

* PEP 550 is based on var.set(..), but you will then implement context managers on top of that.

* PEP 555 is based context managers, but you can implement a var.set(..)​ on top of that if you really need it.

 
Context managers are merely syntactic sugar for try/finally statements, so you can't wave your hands and say a context manager is the only supported API: you *have* to break the semantics down and explain what the try/finally equivalent looks like.



Is this what you're asking?​

​assi = cvar.assign(value)
assi.__enter__()
try:
    # do stuff involving cvar.value
finally:
    assi.__exit__()


As written in the PEP, these functions would have C equivalents. But most C extensions will probably only need cvar.value, and the assignment contexts will be entered from Python.

​––Koos​


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+ Koos Zevenhoven + http://twitter.com/k7hoven +