python function global and local scope confusion [duplicate]

Question

I have a code in which I declare a variable globally. Then inside a function, when I try to use it, it gives an error Unbound variable is not declared My code:

count_url =1

def foo():
   ...
           ttk.Label(canvas1, text=f'{varSongTitle}...Done! {count_url}/{str(var_len)}').pack(padx=3,pady=3)
        root.update()
        count_url = count_url + 1

When I read from here that for bypassing this issue: The issue as I guess was that inside function my globally declared variable was becoming local, I guess because after printing it out I was assigning it to count_url =+ That's why I needed to also decalre it globally inside function as below:

count_url =1

def foo():
   global count_url
   ...
           ttk.Label(canvas1, text=f'{varSongTitle}...Done! {count_url}/{str(var_len)}').pack(padx=3,pady=3)
        root.update()
        count_url = count_url + 1

Now code works perfectly! But I have pair of questions How? Why?. Why it does not behave similarly if I assign global in global scope like

global count_url
count_url=1

def foo():
...

And also How can this be possible, that due to assigning inside the function a value to my global variable, why it becomes local?

Please do not edit questions to add an answer to them - that's not how Stack Overflow works. (I just found this duplicate question and closed it as a duplicate. By the way: my answer there already included the documentation link.) — Karl Knechtel
– Karl Knechtel, Commented Mar 31 at 22:07

Scorpio · Accepted Answer · 2023-02-04 06:13:11Z

3

The default behavior of Python is to create a new variable in the function scope without checking the global scope for a similarly named variable.

The global declaration inside the function tells Python that you want to use the variable declared in the outer scope instead of creating a new one.

Adding a reference to the official Python documentation, from a comment: https://docs.python.org/3/faq/programming.html#why-am-i-getting-an-unboundlocalerror-when-the-variable-has-a-value

edited Feb 4, 2023 at 6:13

answered Feb 3, 2023 at 12:31

Scorpio

1,1441 gold badge12 silver badges28 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

xlmaster Over a year ago

` use the variable declared in the outer scope` I thought declaring global inside function is for using it in outer scope. But, now your words describe it as, python looks for that variable in outer scope

Scorpio Over a year ago

Yes, you understood what I said correctly.

xlmaster Over a year ago

Thanks, I will also look for it in documentations

xlmaster Over a year ago

docs.python.org/3/faq/…

Collectives™ on Stack Overflow

python function global and local scope confusion [duplicate]

1 Answer 1

4 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Linked

Related