From: Steven D'Aprano <steve+comp.lang.pyt...@pearwood.info>
On Sun, 24 Jun 2018 00:37:36 +0100, Bart wrote:
> Do you mean that if the same 'def' block is re-executed, it will create
> a different instance of the function? (Same byte-code, but a different
> set of everything else the function uses.)
That's not as slow as you think it is. Everything that can be is pre- prepared
and assembling them is pretty fast:
py> import dis
py> dis.dis(lambda x: lambda n: x*n)
1 0 LOAD_CLOSURE 0 (x)
3 BUILD_TUPLE 1
6 LOAD_CONST 1 (<code object <lambda> at
0xb78b6430, file "<stdin>",
line 1>)
9 LOAD_CONST 2 ('<lambda>.<locals>.<lambda>')
12 MAKE_CLOSURE 0
15 RETURN_VALUE
How else can you get functions where the definition is not known until runtime,
unless you assemble them at runtime?
> Wow. (Just think of all the times you write a function containing a neat
> bunch of local functions, every time it's called it has to create a new
> function instances for each of those functions, even if they are not
> used.)
That's why Pascal-style static nested functions are hardly ever used in Python.
99% of nested functions are closures.
--
Steven D'Aprano
"Ever since I learned about confirmation bias, I've been seeing it everywhere."
-- Jon Ronson
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