Variable scope inside and outside functions - global statement being overridden by assignation unless preceded by reference

[dn]

Jacob,

Please reduce the problem to a small code-set which reproduces the 
problem. If we can reproduce same, then that tells us something. At the 
very least, we can experiment without having to expend amounts of time 
in a (likely faulty) bid to reproduce the same environment.

Also, code is the ultimate description!


Perhaps start with a small experiment:

- after l_servers is created, print its id()
- after the global statement, print its id()
- after the clear/reassignment, print its id()

Is Python always working with the same list?
Please advise...


On 6/03/24 07:13, Jacob Kruger via Python-list wrote:
> Hi there
> 
> 
> Working with python 3.11, and, issue that confused me for a little 
> while, trying to figure out what was occurring - unless am completely 
> confused, or missing something - was that, for example, when having 
> pre-defined a variable, and then included it in the global statement 
> inside a function, that function was still referring to a completely 
> local instance, without manipulating outside variable object at all 
> unless I first executed a form of referral to it, before then possibly 
> assigning a new value to it.
> 
> 
> Now, this does not seem to occur consistently if, for example, I just 
> run bare-bones test code inside the python interpreter, but consistently 
> occurs inside my actual testing script.
> 
> 
> Basically, in a file with python code in that am using for a form of
> testing at the moment, at the top of the file, under all the import
> statements, I initiate the existence of a list variable to make use of
> 
> later:
> 
> 
> # code snippet
> 
> l_servers = []
> 
> # end of first code snippet
> 
> 
> Then, lower down, inside a couple of different functions, the first line
> inside the functions includes the following:
> # code snippet
>      global l_servers
> # end code snippet
> 
> That should, in theory, mean that if I assign a value to that variable
> inside one of the functions, it should reflect globally?
> 
> However, it seems like that, while inside those functions, it can be
> assigned a new list of values, but if I then return to the scope outside
> 
> the functions, it has reverted back to being an empty list = []?
> 
> 
> The issue seems to specifically (or not) occur when I make a call to one 
> function, and, in the steps it's executing in one context, while it's 
> not doing anything to the list directly, it's then making a call to the 
> second function, which is then meant to repopulate the list with a brand 
> new set of values.
> 
> 
> Now, what almost seems to be occurring, is that while just manipulating 
> the contents of a referenced variable is fine in this context, the 
> moment I try to reassign it, that's where the issue is occurring .
> 
> 
> Here are relevant excerpts from the file:-
> 
> 
> # start code
> 
> # original assignation in main part of file
> 
> l_servers = []
> 
> 
> # function wich is initially being executed
> 
> def interact():
>      global l_servers
>      # extra code inbetween choosing what to carry out
> 
>      # ...
> 
>      # end of other code
> 
>      bl_response, o_out = list_servers()
> 
>      if bl_response: # just make sure other function call was successful
> 
>          l_servers.clear() # first make reference to global variable
> 
>          for srv in o_out: l_servers.append(srv) # now re-populate items
> 
>      # end code snippet from inside interact function
> 
> # end of interact function
> 
> # end of code snippet
> 
> 
> That other function being called from within, list_servers() was 
> initially just trying to populate the values inside the global list 
> variable itself, but was ending up in a similar fashion - reverting to 
> initial empty value, but, the above now seems to work, as long as I 
> first make reference to/manipulate/work with global variable instead of 
> just trying to reassign it a brand new value/set of items?
> 
> 
> So, am I missing something obvious, have I forgotten about something 
> else - yes, know that if was working from within an embedded function, I 
> might need/want to then use the nonlocal statement against that variable 
> name, but, honestly, just not sure how this can be occurring, and, it's 
> not just with this one list variable, etc.?
> 
> 
> If I try simple test code from within the python interpreter, using 
> different types of variables, this does also not seem to be the same all 
> the time, but, don't think it can relate to an iterable like a list, or 
> else, just in case, here is the code snippet with all the import 
> statements from the top of that file, in case something could be 
> overriding standard behaviour - not likely in this context, but, really 
> not sure what's occurring:
> 
> # import code snippet
> 
> import requests, time
> from requests.auth import HTTPBasicAuth
> import psutil as psu
> import pytz
> import bcrypt
> from copy import copy
> from datetime import datetime, timedelta, timezone
> from dateutil.parser import parse
> 
> # end of import snippet
> 
> 
> Thanks if you have any ideas/thoughts on the matter
> 
> 
> Jacob Kruger
> +2782 413 4791
> "Resistance is futile!...Acceptance is versatile..."
> 
> 

-- 
Regards,
=dn