[Python-Dev] Scope, not context? (was Re: PEP 550 v3 naming)
Yury Selivanov
yselivanov.ml at gmail.com
Fri Aug 25 10:18:55 EDT 2017
Right, Nick, I missed the part that you want to have a file-like
wrapper stored in sys.std* streams that would redirect lookups/calls
to the relevant real file-object in the current context (correct?)
I has a similar idea when I discovered that PEP 550 can't be used
directly to fix sys.std* streams redirection. Another idea:
1. We alter PyModule to make it possible to add properties (descriptor
protocol, or we implement custom __getattr__). I think we can make it
so that only sys module would be able to actually use it, so it's not
going to be a new feature -- just a hack for CPython.
2. We make sys.std* attributes properties, with getters and setters.
3. sys.std* setters will: issue a DeprecationWarning; set whatever the
user wants to set in a global variable + set a flag (let's call it
"sys.__stdout_global_modified") that sys.std* were modified.
4. sys.std* getters will use PEP 550 to lookup when
__stdout_global_modified is false. If it's true -- we fallback to
globals.
5. We deprecate the current API and add new APIs for the redirection
system that uses PEP 550 explicitly.
6. In Python 4 we remove the old sys.std* API.
Thit is still *very* fragile: any code that writes to sys.stdout
breaks all assumptions. But it offers a way to raise a warning when
old-API is being used - something that we'll probably need if we add
new APIs to fix this problem.
Yury
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