bpo-32596: Lazy import concurrent.futures.process and thread

[methane]

https://bugs.python.org/issue32596

[asvetlov]

Don't follow why do you need globals here?

[methane]

Once ProcessPoolExecutor is accessed, it's assigned to module global.
Next time, __getattr__ is not called, because futures has ProcessPoolExecutor now.

[methane]

>>> import concurrent.futures
>>> concurrent.futures.__dict__.keys()
dict_keys(['__name__', '__doc__', '__package__', '__loader__', '__spec__', '__path__', '__file__', '__cached__', '__builtins__', '__author__', '_base', 'FIRST_COMPLETED', 'FIRST_EXCEPTION', 'ALL_COMPLETED', 'CancelledError', 'TimeoutError', 'BrokenExecutor', 'Future', 'Executor', 'wait', 'as_completed', '__all__', '__dir__', '__getattr__'])
>>> from concurrent.futures import *
>>> concurrent.futures.__dict__.keys()
dict_keys(['__name__', '__doc__', '__package__', '__loader__', '__spec__', '__path__', '__file__', '__cached__', '__builtins__', '__author__', '_base', 'FIRST_COMPLETED', 'FIRST_EXCEPTION', 'ALL_COMPLETED', 'CancelledError', 'TimeoutError', 'BrokenExecutor', 'Future', 'Executor', 'wait', 'as_completed', '__all__', '__dir__', '__getattr__', 'process', 'ProcessPoolExecutor', 'thread', 'ThreadPoolExecutor'])

[asvetlov]

Neat trick!

[ilevkivskyi]

Actually, this pattern is explicitly discouraged and my not work in other implementations, see https://docs.python.org/3.7/reference/simple_stmts.html#the-global-statement

Names listed in a global statement must not be defined as formal parameters or in a for loop control target, class definition, function definition, import statement, or variable annotation.
CPython implementation detail: The current implementation does not enforce some of these restrictions, but programs should not abuse this freedom, as future implementations may enforce them or silently change the meaning of the program.

There is however no recommendations on what is the recommended pattern instead.

[methane]

@ilevkivskyi Thanks, I didn't know that.
I'll fix it before 3.7b1

[asvetlov]

if/elif/else would be a little faster maybe?

[methane]

dis shows exactly same bytecode for both.

[asvetlov]

Ok