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[Senthil Kumaran]
> I am unaware of the optimization technique you refer to as
> well, it will helpful if you could point to any resource.
It's an old trick since the very first Pythons: global lookups are
much slower than local lookups (the difference between the LOAD_GLOBAL
and LOAD_FAST opcodes in CPython). Putting:
 ..., _fast=slow, ...
in an argument list means we endure the slow lookup (of `slow`) only
once, when the function is first defined. When the function is
_called_, that binding is available via the local (much faster lookup)
variable `_fast`.
Purely a speed trick, but can make a real difference in very heavily
used functions.
And it's a Good Idea to put a leading underscore on such arguments.
It's never intended that users pass values for them.