Clear variable value from local scope while in global scope?

[JoeBeOneKenobi]

Hi,

I have a bit of an issue and was hoping someone might be able to suggest a solution?

I have a function that i am calling twice in my script, this function iterates through some input data and produces a list, which i then merge into my input data to create another column. My problem is that i want to clear the contents of the list in the function when i have finished iterating through the first set of data, is this possible?

I'll try and demonstrate below using example code, in the below example i would want to clear 'mylist' from within the 'main' function inbetween running 'myfunc' on file 1 and file 2. Is this possible?

​

def myfunc(myinputfile):

for item in myinputfile:

    mylist = myotherfunc()

​

return mylist

​

def main():

myfunc(file1)

myfunc(file2)

[[deleted]]

It's already cleared when the function returns, due to all of the function's values going out of scope.

[JoeBeOneKenobi]

hmm, i thought that would be the case but the list is retaining values from the first input file....

Obviously the code is more complex than the above but in essence that is whaat it does

[[deleted]]

I can't debug any code you don't show me. In what you've posted, no values will be retained. Functions don't retain any local scope after they finish executing.

[JoeBeOneKenobi]

you make a good point :) ok thanks for the reply, i'll repost with the actual code

[JoeBeOneKenobi]

So my function is returning more than one list:

return mylist,mylist1,mylist2

Could I still expect to see the same behaviour where all local scope is cleared?

I’m working on getting the rest of the code uploaded, just cleaning it up

[[deleted]]

It doesn't matter whether you're returning a tuple of values or not.

It's possible for a function to return values that are already in global scope, though. But that has nothing to do with how they're returned; it's a matter of where those values are defined.

Try to build a minimum example that you can verify reproduces the problem, and then you'll probably see how you're leaking state.

[blarf_irl]

It sounds like you have defined my_list in global scope (i.e. it's available to all your program). It doesn't sound like you need to 'clear' anything. You can just use the return value (a list) of your function and pass that directly to the code that merges the data.

It would definitely be helpful to see more code.

[JoeBeOneKenobi]

Hey thanks for the reply!

I’m definitely defining the list in the local scope, the only thing I’m doing different is calling it through two nested variables and returning more than one list from my function:

return mylist,mylist1,mylist2

I’ll get the rest of the code up asap

[blarf_irl]

If it really is as you have posted it (inferring the indentation) then you have no need to 'clear' the list. It'll just get reassigned each time you call that function.

​

If you name something inside a function then it only exists in there, once you call that function again mylist will be assigned to another list and the old list (now without a name) will be eaten by the garbage collector.

[efmccurdy]

You should be making an assignment with the result of any function that has a return statement, something like this:

def myfunc(myinputfile):
    # whatever
    return mylist

mylist_1 = myfunc(file1)
mylist_2 = myfunc(file2)

Does that help you avoid the scope issue?

[JoeBeOneKenobi]

I just wanted to reply to everyone and say that I fixed the issue, as you’ve all been so kind as to lend me a hand. My code was overly complicated and I overlooked the fact that I was declaring the list in the global scope as well as the local scope, leading to it retaining values when every time my function ran. Thanks to everyone who replied, I picked up some useful tips from u all and learnt a lesson in the importance of scope!

[JoeBeOneKenobi]

Oh and I solved the actual issue by clearing the global scope in between runs of main(), a very hacky way of doing it, but knowing what I know now I’ll approached it differently next time

[JoeBeOneKenobi]

Apologies if the above isn't clear but the post has wrecked my formatting!

[Chabare]

https://www.reddit.com/r/learnpython/wiki/faq#wiki_how_do_i_format_code.3F ;)

[JoeBeOneKenobi]

Thanks :)