Iterating through a dictionary for a specific outcome

I have a dictionary in which the keys represent the categories and their values the item-lists for each category, like so:

d = {category_a: [item_a, item_b, item_c], category_b: [item_d, item_e]}

I want to iterate through the dictionary for the following result:

category_a
· item_a
· item_b
· item_c
category_b
· item_d
· item_e

The formatting with break-lines and such seem to work. My issue is that I only get to the following result:

category_a
· item_a
· item_b
· item_c
· item_d
· item_e
category_b
· item_a
· item_b
· item_c
· item_d
· item_e

I understand that my code (see below) iterates though all items for all keys, which probably causes the issue. Everything else have I tried leads to errors or one-letter-per-line outcome. I want to place the outcome in a PySimpleGUI Multiline. That's why I intend to place it in a string.

Here is my basic code-structure:

def display():

    d = {category_a: [item_a, item_b, item_c], category_b: [item_d, item_e]}
    
    output = ""

    for k in d.keys():
        output += k + "\n"

        for key, val in d.items():
            for v in val:
                output += " · " + v + "\n"

    return output 

I tried, in the second for loop, to only access the values of the key used above (first loop) but can't get it working: Either I only get the item-list - not the items in it - or I produce an error.

You can call method print of Multiline element directly.

import PySimpleGUI as sg

def display(ml):
    d = {
        "category_a": ["item_a", "item_b", "item_c"],
        "category_b": ["item_d", "item_e"],
    }
    for key, items in d.items():
        ml.print(key)
        for item in items:
            ml.print(f". {item}")

sg.set_options(font=("Courier New", 12, "bold"))
layout = [[sg.Multiline("", size=(40, 10), key='-ML-')]]
window = sg.Window('Title', layout, finalize=True)
display(window['-ML-'])
window.read(close=True)

Here is the corrected code:

def display():

    d = {'category_a': ['item_a', 'item_b', 'item_c'], 'category_b': ['item_d', 'item_e']}
    
    output = ""

    for k in d.keys():    # for k in d:  also works
        output += k + "\n"
        for v in d[k]:
            output += " · " + v + "\n"

    return output

def display():

    d = {"category_a": ["item_a", "item_b", "item_c"], "category_b": ["item_d", "item_e"]}
    
    output = ""

    for k,v in d.items():
        output += k + "\n"
        for val in v:
            output += " · " + val + "\n"
    return output

The value of the dict is a list, so just iterate though the list

Hope this helps.
Keep the good work!

def display():
    d = {"category_a": ["item_a", "item_b", "item_c"], "category_b": ["item_d", "item_e"]}

    output = ""
    for key, val in d.items():
        output += key + "\n"
        for v in val:
            output += " · " + v + "\n"
    return output

if __name__ == '__main__':
    print(display())

Instead of making multiple calls to print() rather build a list of what needs to be printed. Something like this:

def display(d):
    out = []
    for k, v in d.items():
        out.append(k)
        out += [f' · {_v}' for _v in v]
    print(*out, sep='\n')

d = {'category_a': ['item_a', 'item_b', 'item_c'], 'category_b': ['item_d', 'item_e']}

display(d)

Output:

category_a
 · item_a
 · item_b
 · item_c
category_b
 · item_d
 · item_e