Few questions here

Hey, let's see what I can answer with my really fuzzy memory of this course. :)

1. Could we define search_query=None in def view_entries(search_query=None): as a variable instead of a function argument? We did so in

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

What is the difference?

In the menu_loop, you're waiting for input from the user. It's not logical to provide an argument to the function up front. But with viewing entries, we have two ways of using the function: either viewing everything or viewing things that match the search query. So the difference is the purpose of the function and how it's applied.

Could you use a variable inside of the function and ask the user for search terms? Sure, but that means searching requires yet another step from the users: choose view entries, then choose to search (you'd have to add this), and then enter the search term.

1. Why don't we use __init__ method in the Entry class?

It doesn't need one.

1. Which function creates the DB - SqliteDatabase('diary.db')? As it says:

def initialize():
    """Create the database and the table if they don't exist.""" <---
    db.connect()
    db.create_tables([Entry], safe=True)

My understanding is that it connects to the already existing db and creates the table with two columns by calling the class Entry.

If the database exists, Peewee will connect to it. If it doesn't, Peewee will attempt to create the database.

4.When is the timestamp created? Is it here:

if data:
        if input('Save entry? [Yn] ').lower() != 'n':
            Entry.create(content=data) <---
            print('Saved successfully')

In this case my logic says that it should be:

class Entry(Model):
    content = TextField()
    timestamp = DateTimeField()

to create two empty columns and then:

if data:
        if input('Save entry? [Yn] ').lower() != 'n':
            Entry.create(content=data, timestamp=datetime.datetime.now) <---
            print('Saved successfully')

I tried and it did not work.

In my reference code, the Entry class' timestamp field has a default value. This value is used if one isn't provided.

Yours fails there because you're providing the field a function/method (now is a method on the datetime object) instead of a datetime instance. In the field, thedefault is provided with the parentheses because the model will call it when it instantiates an instance.