Re: Await expressions

ram@zedat.fu-berlin.de (Stefan Ram) writes:

|await_expr ::= "await" primary
|Suspend the execution of coroutine on an awaitable object.

  My ideas of language specifications are that they should
  contain all the information to write an implementation of the
  language. I am not sure whether the Python Language Reference
  already fullfils this criterion. BUT I have made one step
  in the direction of better understanding "await":

  main.py

import dis

def f(): return g()

dis.dis( f )
print()

async def f(): return await g()

dis.dis( f )

  sys.stdout

3           0 LOAD_GLOBAL              0 (g)
            2 CALL_FUNCTION            0
            4 RETURN_VALUE

8           0 LOAD_GLOBAL              0 (g)
            2 CALL_FUNCTION            0
            4 GET_AWAITABLE
            6 LOAD_CONST               0 (None)
            8 YIELD_FROM
           10 RETURN_VALUE

  . So, now it's down to finding documentation for the "GET_AWAITABLE"
  and "YIELD_FROM" opcodes! One can guess that GET_AWAITABLE just gets
  a kind of reference to the coroutine g. So the core of await must be
  YIELD_FROM. Web:

|In Python 3.11 and above, the YIELD_FROM opcode is replaced
|by a SEND + YIELD_VALUE while loop, as documented in the
|SEND(target_delta).

  . Oh, this seems to be a moving target!

|# yield from subgenerator is implemented as the following loop
|# (with None initially at the top of the stack)
|#
|# SEND (sends the top of stack to the subgenerator)
|# YIELD_VALUE (returns the yielded value to the caller)
|# JUMP_BACKWARDS (to SEND)

  Ok, but this just seems to spell out what "YIELD_FROM" does,
  so it should still be true that "await" boils down to "YIELD_FROM".
  (Yes, Greg already kindly answered something to that effect.)