DEV Community: Kenn-stack

Demystifying Iterables and Iterators in Python

Kenn-stack — Thu, 25 May 2023 02:03:09 +0000

Two fundamental concepts in Python's iteration protocol are iterables and iterators. Although these terms may sound similar, they have distinct roles and behaviours. In this article, we will explore the key differences between iterables and iterators and how they help us efficiently traverse data in Python.

Understanding Iterables

In Python, an iterable is any object capable of returning its elements one at a time. It represents a collection of items that can be iterated upon. Examples of built-in iterables include lists, tuples, strings, and dictionaries.

Let's consider a simple example of a list:

my_list = [1,2,3,4]
for i in my_list:
    print (i)

Output:

Perhaps more elementarily, and for the purpose of explanation, we can consider an iterable as an object with an __iter__() method.

print(dir(my_list))

Output:

['__add__', '__class__', '__class_getitem__', '__contains__', '__delattr__', '__delitem__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__iadd__', '__imul__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__rmul__', '__setattr__', '__setitem__', '__sizeof__', '__str__', '__subclasshook__', 'append', 'clear', 'copy', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']

This is where things get interesting!
The __iter__() method basically returns an Iterator object. This object is what is looped over by the for keyword.

Have a look at this:

my_list = [1,2,3,4]
my_iterator_list = my_list.__iter__()
print(i_my_list)

Output:

<list_iterator object at 0x7f3abd6eaa30>

But we are getting ahead of ourselves...

What are Iterators?

Iterators are objects that implement the iteration protocol, enabling iteration over an iterable object. They maintain the state of the iteration and provide a mechanism for accessing elements sequentially.

Woah! That's a lot of “Itera-”s. But what do we mean?

Essentially, Iterators are what make iteration (looping) possible. Your list or string (Iterable) is first converted to an Iterator object before it can be iterated over. We said earlier, this is done through the __iter__() method. Python also has a built-in iter() function that does the same thing.

my_list = [1,2,3,4]
my_iterator_list = iter(my_list)
print(i_my_list)

Output:

<list_iterator object at 0x7f3abd6eaa30>

An Iterator, in addition to having an __iter__() method like the Iterable, also has its characteristic __next__() method.

print(dir(my_iterator_list))

Output:

['__class__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__length_hint__', '__lt__', '__ne__', '__new__', '__next__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__setstate__', '__sizeof__', '__str__', '__subclasshook__']

The __next__() method returns the next element in the iteration. This method raises the StopIteration exception when there are no more elements left to iterate. And of course, Python has a built-in next() function.

my_list = [1,2,3,4]
my_iterator_list = iter(my_list)

print(next(my_iterator_list))
print(next(my_iterator_list))
print(next(my_iterator_list))
print(next(my_iterator_list))
print(next(my_iterator_list))

Output:

1
2
3
4
Traceback (most recent call last):
  File "/home/kenn-stack/python test.py", line 32, in <module>
    print(next(my_iterator_list))
StopIteration

Iterator and Iterable Relationship

An important point to note is that an Iterator is also an Iterable, but not all Iterables are Iterators.

N.B: The __iter__() method of an Iterator just returns self since it is already an iterator.

A Practical Example

Let us consider this custom bit of code that mimics the Python for operation. It also catches the StopIteration exception.

my_list = [1,2,3,4]
my_iterator_list = iter(my_list)

while True:
    try:
        looped = next(my_iterator_list)
        print(looped)
    except StopIteration:
        break

Output:

Just as the first example!

And that's it. Don't forget to like and comment.
Ciao
Till next time…

Simplify if-else statements with Objects

Kenn-stack — Tue, 16 May 2023 09:02:42 +0000

If/else statements can prove very useful in performing conditional operations, yet, they usually become very unwieldy very fast!

Consider this simple function:

function studentGrade(score){
    if(score > 50){
        return 'Pass!';
    };

    else{
        return 'Fail!';
    };
};

For a simple operation like this, an if/else block would make sense. But suppose you had a slightly larger set of data, like the one below:

function elementColor(color){
    if (color ==='blue'){
        return '#00f';
    }

    else if(color === 'black'){
        return '#000';
    }

    else if (color === 'red'){
        return '#f00';
    }

    else if(color === 'gray'){
        return '#999';
    }

    else if(color === 'orange'){
        return '#ff6600';
    }

    else{
        return '#fff';
    }
};

I'm sure you are getting the idea. For every new colour entry, the block gets bigger and more prone to error.

This is where Objects come in. By situating your data entries in an Object, you can perform the same operation.

Like this:

function setElementColor(color){
    const colorPalette = {
        blue: '#00f',
        black: '#000',
        red: '#f00',
        gray: '#999',
        orange: '#ff6600',
    };
    return colorPalette[color] || '#fff';    
};

And that's it. Don't forget to like and comment!
Ciao.
Till next time...

JWT with Djoser

Kenn-stack — Tue, 02 May 2023 07:46:24 +0000

Introduction

Djoser is a library that provides a set of Django Rest Framework(DRF) views to handle basic actions such as registration, login, logout, password reset and account activation. It also works with a custom user model.

In this article, I'll show you how to implement JSON Web Token(JWT) authentication with Djoser.

Please note that I write this article assuming you are comfortable with Django and Django Rest Framework. You don't need to be an expert; as long as you can set up a Django project, you'll be just fine.

Setting It Up

Per best practices, make sure you have your virtual environment activated.Then proceed to install Djoser by typing this in your terminal.

pip install -U djoser

Next, you'll install Simple JWT. This is the package we would use to implement our JWT authentication.

pip install djangorestframework-simplejwt

After installation is complete, proceed to your settings.py to configure the package. Append the following code to the bottom of the file:

from datetime import timedelta

SIMPLE_JWT = {
    'ACCESS_TOKEN_LIFETIME': timedelta(minutes=15),
    'REFRESH_TOKEN_LIFETIME': timedelta(days=1),
    'AUTH_HEADER_TYPES': ('JWT',),
    'AUTH_HEADER_NAME': 'HTTP_AUTHORIZATION',
    'USER_ID_FIELD': 'id',
    'USER_ID_CLAIM': 'user_id',
}

ACCESS_TOKEN_LIFETIME: A datetime.timedelta object which specifies how long access tokens are valid.

REFRESH_TOKEN_LIFETIME: A datetime.timedelta object which specifies how long refresh tokens are valid.

AUTH_HEADER_TYPES: The authorization header type(s) that will be accepted for views that require authentication. For example, a value of 'JWT' means that views requiring authentication would look for a header with the following format:Authorization: JWT <token>. This setting may also contain a list or tuple of possible header types (e.g. ('JWT', 'Bearer')).

AUTH_HEADER_NAME: The authorization header name to be used for authentication. The default is HTTP_AUTHORIZATION which will accept the Authorization header in the request.

USER_ID_FIELD: The database field from the user model that will be included in generated tokens to identify users.

USER_ID_CLAIM: The claim in generated tokens which will be used to store user identifiers. For example, a setting value of 'user_id' would mean generated tokens include a “user_id” claim that contains the user’s identifier.

For more on configuring Simple JWT, you can refer to the docs.

Wrapping Up

Djoser already has inbuilt urls to manage JWT Authentication. These are:

/jwt/create/: This returns access_tokens and refresh_tokens when you pass login credentials.

/jwt/refresh/: Use this endpoint to refresh JWT.

/jwt/verify/: Use this endpoint to verify JWT.

Simple JWT takes care of all the logic under the hood.

And that's it. Don't forget to like and comment.
Ciao.
Till next time…