mlog: make mlog helper take once keyword argument

[dcbaker]

We really want to have this in the log method as well.

Fixes: #8002

[lgtm-com]

This pull request introduces 1 alert when merging f5c6d4d into 9133748 - view on LGTM.com

new alerts:

• 1 for Use of the return value of a procedure

[lgtm-com]

This pull request introduces 1 alert when merging 5095efd into cef406b - view on LGTM.com

new alerts:

• 1 for Use of the return value of a procedure

[dcbaker]

the LGTM warning is stupid. It's complaining that I'm returning a function that returns None. but it looks like this:

def _fun1() -> None: ...
def _fun2() -> None: ...

def fun(thing: bool = true) -> None:
   if thing:
    return _fun1()
  return _fun2()

Not returning here is odd.

[bonzini]

Why not use else as in the code you are moving? Or returning on a separate line would work too.

[dcbaker]

it's generally considered a code smell in python to use an else when you return from a single if, both because it creates unnecessary indentation, and also because there is a small cost to the else block.