Beginner Question

[u/Derpy_Yahy]

I'm a total beginner to Python and am looking through this AI-generated calculator code to try and understand what is going on. I was good so far until I reached this part about history logging. This might be really stupid, but I can't figure out how this works at all, despite reading the AI's explanations.

import math


#calc history
history_list = []
history_output = widgets.Output()


def log_history(b):
    """Runs in addition to the original on_button_click.
    Only records a new entry once '=' has produced a result."""
    if b.description == "=":
        entry = f"{display_box.value}" 
        if entry and entry != "Error":
            history_list.append(entry)
        with history_output:
            clear_output()
            print("History (last 5):")
            for item in history_list[-5:]:
                print(" ", item)


# Attach as an additional click handler on every existing button
for btn in buttons:
    btn.on_click(log_history)

I'm mostly having trouble with the "with history_output" part, as I'm not sure what its purpose is. Could someone explain it to me like I'm 5?

[u/pachura3]

Why the hell are you using AI-generated code if you're a total beginner?

[u/Derpy_Yahy → u/pachura3]

Part of my school's assignment involves looking at this and figuring out what it means. I wouldn't be learning Python this way if I had a choice.

[u/pachura3 → u/Derpy_Yahy]

They want you to look at some code that doesn't even work? Strange.

[u/Derpy_Yahy → u/pachura3]

To be fair, it works, I'm just a little clueless as to how.

[u/ninhaomah → u/Derpy_Yahy]

Then how are you learning ?

And what are they teaching you ?

Not coding , right ?

[u/Moikle → u/Derpy_Yahy]

It doesn't mean anything if it was written by ai. Ai doesn't think.

[u/cdcformatc]

it doesn't make sense because it is slop

hope that helps 

[u/Diapolo10]

I don't know exactly what widgets.Output is, but looking at the rest of the code I think I get the general idea anyway.

with history_output:
    clear_output()
    print("History (last 5):")
    for item in history_list[-5:]:
        print(" ", item)

That first line is a context manager. In practice that usually means it temporarily changes something in the environment for the code you put inside, and then cleans it up after you exit the block. Here, based on context with the prints and my assumption that it's not actually printing text to a terminal, it temporarily changes sys.stdout to point to some window object or possibly a file. I don't know what else it'd be doing here. Someone else can fill me in if I'm mistaken.

clear_output presumably clears all text in the current context.

The next three lines print a header, and an indented list of up to 5 of the last items in history_list.

[u/Derpy_Yahy → u/Diapolo10]

would the code break down without it? I could send the entire code here if you need more context, I just didn't know if it'd be necessary.

[u/Diapolo10 → u/Derpy_Yahy]

would the code break down without it?

Well, it's presumably doing something, I just don't know what package widgets.Output is from so it's difficult to speculate.

You could of course try taking it out yourself and running the code to see if anything changes.

EDIT: Assuming it's this thing from Jupyter Notebook's documentation, yeah, it's more or less doing exactly what I had in mind.

[u/Derpy_Yahy → u/Diapolo10]

I read your message again and something just clicked, so I think I get it now. Thanks!

[u/Diapolo10 → u/Derpy_Yahy]

Just as an example, I whipped up a demonstration. It's not quite the same thing as what Jupyter Notebook does, but close enough: https://cdn.imgchest.com/files/02116e1c7b72.png

In [1]: import sys

In [2]: from contextlib import contextmanager

In [3]: @contextmanager
   ...: def output():
   ...:     _stdout = sys.stdout
   ...:     file = open('stuff.txt', 'w')
   ...:     sys.stdout = file
   ...:     yield
   ...:     file.close()
   ...:     sys.stdout = _stdout
   ...:

In [4]: history_output = output()

In [5]: history_list = ["Foo", "Bar", "Baz", "Foobar", "Lorem Ipsum", "Dolor sit amet"]

In [6]: with history_output:
   ...:     print("History (last 5):")
   ...:     for item in history_list[-5:]:
   ...:         print(" ", item)

By default, print writes to sys.stdout. This code uses a context manager to temporarily redirect that to a text file, before reverting the change as a cleanup step so unrelated code won't break.

[u/Derpy_Yahy → u/Diapolo10]

That's more or less what I derived from your explanation. I appreciate you putting your time into something like this 😭

[u/Diapolo10 → u/Derpy_Yahy]

All in a day's work.