[Python-Dev] Issues with PEP 482 (1) (original) (raw)

Mark Shannon mark at hotpy.org
Tue Apr 28 20:44:53 CEST 2015

Hi,

I still think that there are several issues that need addressing with PEP 492. This time, one issue at a time :)

"async"

The "Rationale and Goals" of PEP 492 states that PEP 380 has 3 shortcomings. The second of which is: """It is not possible to natively define a coroutine which has no yield or yield from statements.""" This is incorrect, although what is meant by 'natively' is unclear.

A coroutine without a yield statement can be defined simply and concisely, thus:

@coroutine def f(): return 1

This is only a few character longer than the proposed new syntax, perfectly explicit and requires no modification the language whatsoever. A pure-python definition of the "coroutine" decorator is given below.

So could the "Rationale and Goals" be correctly accordingly, please. Also, either the "async def" syntax should be dropped, or a new justification is required.

Cheers, Mark.

#coroutine.py

from types import FunctionType, CodeType

CO_COROUTINE = 0x0080 CO_GENERATOR = 0x0020

def coroutine(f): 'Converts a function to a generator function' old_code = f.code new_code = CodeType( old_code.co_argcount, old_code.co_kwonlyargcount, old_code.co_nlocals, old_code.co_stacksize, old_code.co_flags | CO_GENERATOR | CO_COROUTINE, old_code.co_code, old_code.co_consts, old_code.co_names, old_code.co_varnames, old_code.co_filename, old_code.co_name, old_code.co_firstlineno, old_code.co_lnotab, old_code.co_freevars, old_code.co_cellvars) return FunctionType(new_code, f.globals)

P.S. The reverse of this decorator, which unsets the flags, converts a generator function into a normal function. :?

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