So, this does not make sense to me in terms of the following snippet
from the official python docs page:
https://docs.python.org/3/faq/programming.html
"In Python, variables that are only referenced inside a function are
implicitly global. If a variable is assigned a value anywhere within the
function’s body, it’s assumed to be a local unless explicitly declared
as global."
So, I would then assume that if I explicitly include a variable name
inside the global statement, then even just assigning it a new value
should update the variable in the global context, outside the function?
Unless this is something that changed from 3.11 to 3.12 - since that
snippet is more or less referring to 3.12, but, don't think it was
changed in any way?
Jacob Kruger
+2782 413 4791
"Resistance is futile!...Acceptance is versatile..."
On 2024/03/06 14:55, Jacob Kruger wrote:
Ok, simpler version - all the code in a simpler test file, and working
with two separate variables to explain exactly what am talking about:
# start code
from datetime import datetime, timezone, timedelta
from copy import copy
# initialise original values
dt_expiry = datetime.strptime("1970-01-01 00:00", "%Y-%m-%d
%H:%M").replace(tzinfo=timezone.utc)
l_test = [1, 2, 3]
def do_it():
global dt_expiry, l_test # asked python to refer to global
variables for both
# assign new value immediately
dt_expiry = datetime.now()+timedelta(minutes=5)
print(dt_expiry.strftime("%Y-%m-%d %H:%M")) # just to show new
value has been assigned
# grab copy of list for re-use of items
l_temp = copy(l_test)
# following line means l_test will later on retain value in global
scope because it was manipulated inside function instead of just
assigned new value
l_test.clear()
# replace original set of values
for i in l_temp: l_test.append(i)
# add new item
l_test.append(99)
# end of do_it function
# end code
If you import the contents of that file into the python interpreter,
dt_expiry will start off as "1970-01-01 00:00", and, if you execute
do_it function, it will print out the new value assigned to the
dt_expiry variable inside that function, but if you then again check
the value of the dt_expiry variable afterwards, it's reverted to the
1970... value?
If I take out the line that removes values from l_test #
l_test.clear() # before appending new value to it, then it will also
not retain it's new/additional child items after the function exits,
and will just revert back to [1, 2, 3] each and every time.
In other words, with some of the variable/object types, if you use a
function that manipulates the contents of a variable, before then
re-assigning it a new value, it seems like it might then actually
update/manipulate the global variable, but, either just calling purely
content retrieval functions against said objects, or assigning them
new values from scratch seems to then ignore the global scope
specified in the first line inside the function?
Hope this makes more sense
Jacob Kruger
+2782 413 4791
"Resistance is futile!...Acceptance is versatile..."
On 2024/03/05 20:23, dn via Python-list wrote:
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..."
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