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

[Mark Shannon]

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. :?