I don't understand the relationship between the menu OrderDict tuple, choice assignment, and the if choice in menu bloc

Hi Pete

I took this module a several weeks ago I think and re-watched it now. This is how I understand all of it.

This thing here value.__doc__ prints out the docstring of a value. In our case the values are actually functions. The docstring for add_entry is """Add an entry.""".

In this next block we have the choices where, for example, 'a' is the key and the corresponding value is add_entry which is actually a function as mentioned before. In ordered dictionaries we add things as a list. In regular dictionaries we would use a colon instead of a comma like ('a': add_entry).

menu = OrderedDict([
        ('a', add_entry),
        ('v', view_entries),
    ])

You can loop through the keys and values in the ordered dictionary just like in a regular dictionary. Here's an example for you:

menu = OrderedDict([
        ('a', 'add_entry'),
        ('v', 'view_entries'),
    ])

for key in menu.keys():
    print(key)

for value in menu.values():
    print(value)

for key, value in menu.items():
    print(f"The key is '{key}' and the value is '{value}'.")

The output for the above is:

a
v
add_entry
view_entries
The key is 'a' and the value is 'add_entry'.
The key is 'v' and the value is 'view_entries'.

So the items in menu.items(): are the keys and values in the variable menu.

I played around with the code in PyCharm and check this - I changed the docstring for this function def add_entry()::

from peewee import *
from collections import OrderedDict

def menu_loop():
    """Show the menu"""
    choice = None

    while choice != 'q':
        print("Enter 'q' to quit.")
        for key, value in menu.items():
            print('{}) {}'.format(key, value.__doc__))
        choice = input('Action: ').lower().strip() 

        if choice in menu:
            menu[choice]()


def add_entry():
    """Just a test."""


def view_entries():
    """View previous entries."""


menu = OrderedDict([
        ('a', add_entry),
        ('v', view_entries),
    ])

menu_loop()

The output for the above is:

Enter 'q' to quit.
a) Just a test.
v) View previous entries.
Action: 

If you lose the parens after menu[choice] the statement will have no effect. For example, menu[a] is the function add_entry (as we can see from the menu) and we need to run it so this is why we need to use the parens here. So it's like menu[a]() is equal to add_entry().

And we don't want parens here ('a', add_entry()), since we do not want to call the function. If we used parens then the output would be:

Enter 'q' to quit.
a) None
v) View previous entries.
Action: 

So a) would be None since we are calling the function add_entry and there is nothing to return. The function add_entry has only a docstring and nothing else.

I am not entirely sure if this all helps. It's a bit difficult to explain in writing.