[Python-Dev] Must objects with enter/exit also supply context? (original) (raw)

Guido van Rossum guido at python.org
Wed Apr 26 05:09:34 CEST 2006

On 4/25/06, Phillip J. Eby <pje at telecommunity.com> wrote:

At 05:20 PM 4/25/2006 -0700, Guido van Rossum wrote: >I would augment #1 to clarify that if you have enter and exit >you may not have context at all; if you have all three, >context must return self.

Well, requiring the context allows us to ditch the otherwise complex problem of why @contextfactory functions' return value is usable by "with", without having to explain it separately.

Really? I thought that that was due to the magic in the decorator (and in the class it uses). In this case the use of magic is fine by me; I know I could reconstruct it from scratch if I had to (with only one or two bugs :-) but it's convenient to have it in the library. The primary use case is this:

@contextfactory def foo(): ...

with foo(): ...

but a secondary one is this:

class C: ... @contextfactory def context(self): ...

with C(): ....

Because of these two different uses it makes sense for @contextfactory to return an object that has both context and enter/exit methods.

But that still doesn't explain why we are recommending that everything providing enter/exit must also provide context! I still think we should take it out.

-- --Guido van Rossum (home page: http://www.python.org/~guido/)

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