Global VS Local Subroutines

[BlindAnagram]

On 10/02/2022 16:52, Rob Cliffe wrote:
> 
> 
> On 10/02/2022 12:13, BlindAnagram wrote:
>> Is there any difference in performance between these two program layouts:
>>
>>    def a():
>>      ...
>>    def(b):
>>      c = a(b)
>>
>> or
>>
>>    def(b):
>>      def a():
>>        ...
>>      c = a(b)
>>
>> I would appreciate any insights on which layout to choose in which 
>> circumstances.
>>
> The way to answer questions about performance is not to guess (often 
> difficult or impossible), but to measure.  Profiling tools are available 
> to see where a program spends how much of its time.  But a simpler 
> approach might be to try to run the guts of your program 1000 or 1000000 
> times, and find how long it takes with each layout (not with a stopwatch 
> 😁 but getting the program to record the start time, end time and the 
> difference).
> That said, I will venture a guess (or at least, an observation):
>      def a():
>          ...

Thanks for the suggestion, Rob. I considered doing this but it would 
take quite a bit of careful work to be sure of obtaining meaningful 
results so I felt it better to ask the question here in case there was 
an quick answer on performance before doing the hard work.

> is executable code.  It creates the function `a` which did not exist 
> before (or creates the new version if it did).  This takes a certain 
> amount of time.  In your 2nd layout, this overhead occurs every time b() 
> is called.  So I would *guess* that this would be slower.  Of course it 
> depends on how many times b() is called and probably on lots of other 
> things.

This is exactly what I felt too but I then wondered if the code was 
recreated dynamically or was static with just a reference being created 
on each invocation of the parent.  The overhead in this case would be 
negligible. But then I thought 'what about the context for the inner 
function invocation' - maybe its not as simple as this!  Oh dear, I need 
to understand Python's internals.

At which point I asked the question!

    Brian