DEV Community: Morris Mulitu

First Flask app!

Morris Mulitu — Wed, 11 Aug 2021 13:04:12 +0000

If you want to build a web app in Python then it is highly likely that you will use a framework!. A framework "is a code library that makes a developer's life easier when building reliable, scalable, and maintainable web applications" Flask is such a framework in Python.

Flask is relatively a new framework. It has however taken the python web development world by storm. It has become quite popular. It is offering alot of extensibility, flexibility and clean code possibilities.

Why Flask?

Flask is thought to be more pythonic than Django due to the fact that the equivalent Flask web application is more explicit. Ideally, it is also easier to get started with for beginners.

Hello, World! with Flask

from flask import Flask
app = Flask(__name__)


@app.route('/')
def hello_world():
    return 'Hello, World!'

if __name__ == '__main__':
    app.run()

Install the Flask library. This code will show "Hello, World!" on localhost port 5000 if you run it.

Flask startup!

You can install the Flask package from PPI
(Python Package Index)
First make a directory eg, flask_todo and then have the flask package installed. Also install flask-sqlalchemy to facilitate a simpler SQL database connection.
It is best to work in a virtual environment.
Do enter the following commands;

$ mkdir flask_todo
$ cd flask_todo
$ pipenv install --python 3.6
$ pipenv shell
(flask-someHash) $ pipenv install flask flask-sqlalchemy

Just in case you want to make if a Git repo, do run git init here.This will be the project's root. Just incase you intend to codebase to different machines you can have all the setup files in this directory.
The best way to move it is to turn the codebase into an installable Python distribution. While at the root of the project create a setup.py and a directory todo to hold the source code.
An example of the setup.py is as below;

from setuptools import setup, find_packages

requires = [
    'flask',
    'flask-sqlalchemy',
    'psycopg2',
]

setup(
    name='flask_todo',
    version='0.0',
    description='A To-Do List built with Flask',
    author='<Your actual name here>',
    author_email='<Your actual e-mail address here>',
    keywords='web flask',
    packages=find_packages(),
    include_package_data=True,
    install_requires=requires
)

With this you will have all the needed packages in the requires list.Additionally, you'll also have everything you need to set up and install the package in site-packages.

In the todo directory, create init.py and app.py files.The init.py file allows you to import from todo as if it was an installed package. The app.py file will be the application's root. Just in case you are using pipenv you can find your virtual environment with pipenv --venv and set up that environment variable in your environment's active script.

export FLASK_APP=$VIRTUAL_ENV/../todo/app.py
export DEBUG='True'

A little code!

from flask import Flask

app = Flask(__name__)

@app.route('/')
def hello_world():
    """Print 'Hello, world!' as the response body."""
    return 'Hello, world!'

This is a basic Flask application.app is an instance of Flask taking in the name of the script file.
app.route specifies the routes used to access the application.Any view you specify must be decorated by app.route to be a functional part of the application.In this example, when the app is running and accessed at http://domainname/, the user will receive "Hello, World!" as a response.

Connecting the database in Flask

The flask-sqlalchemy package connects a SQL database to a Flask application.You need the database URL to connect to a SQL database.You can use Postgres database.The intermediary to talk to the Postgres database is the psycopg2 package.Include it in the list of required packages in setup.py. The flask-sqlalchemy will recognize Postgres from the database URL. Flask will need the database URL to be part of its central configuration through the SQLALCHEMY_DATABASE_URI attribute.

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'postgres://localhost:5432/flask_todo'
db = SQLAlchemy(app)

You can make use of environment variables to make things easier.They ensures that, no matter what machine the code is on, it will always point tp the right stuff if that stuff is configured in the running environment.
In the same place you declared FLASK_APP, declare a DATABASE_URL pointing to the location of your Postgres database. Development tends to work locally, so just point to your local database.

Your application has a database connection! Awesome

Do enjoy!

Introduction To Python Functions

Morris Mulitu — Tue, 03 Aug 2021 17:27:20 +0000

What is a function in Python?

In Python, a functions are a group of related statements that do specific tasks.
Functions are used to create smaller chunks of code in python making programming more streamlined and organized. This hence makes code more understandable to others who who view it. Most importantly, functions make code less repetitive and enhance reusability.

def function_name(parameters):
    """docstring"""
    statement(s)

Using the example above;

The keyword def indicates the start of the function.
The function name is used to uniquely identify the function.
Parameters / arguments are used to pass values to the function. They however are optional.
The end of the function header is denoted by a colon(:)
The (docstring) segment used above details what the funtion is supposed to do.
There can be an optional return statement to return values from the functions.

Example

def greet(name):
    """
    This function greets to
    the person passed in as
    a parameter
    """
    print("Hello, " + name + ". Good morning!")

Calling a function in python

After defining a python function you can go on to call it from another function, a python prompt or maybe another program.
Type the function name and parameters to call it.

>>>greet('Morris')
Hello, Morris. Good morning!

Complete function and its calling;

def greet(name):
    """
    This function greets to
    the person passed in as
    a parameter
    """
    print("Hello, " + name + ". Good morning!")

greet('Morris')

Output;

Hello, Morris. Good morning!

Docstrings

The documentation string or docstring is the first string after the function header. It details what the specific function does. It is optional but hightly recommended. Use triple quotes to enable the docstrings to span over multiple lines.

Return statement

Used to exit the functions and go back to w herever it was called from.

return [expression_list]

A return statement can contain an expression that gets evaluated and the value is returned. If there is no expression in the statement or the return statement itself is not present inside a function, then the function will return the None object.

Example

>>> print(greet("May"))
Hello, May. Good morning!
None

Here, None is the returned value since greet() directly prints the name and no return statement is used.

Example of return

def absolute_value(num):
    """This function returns the absolute
    value of the entered number"""

    if num >= 0:
        return num
    else:
        return -num


print(absolute_value(2))

print(absolute_value(-4))

Output

2
4

Python Function Arguments

You can define a function that takes variable number of arguments.

def greet(name, msg):
    """This function greets to
    the person with the provided message"""
    print("Hello", name + ', ' + msg)

greet("Monica", "Good morning!")

Output

Hello Monica, Good morning!

Here, the function greet() has two parameters.
If we call it with a different number of arguments, the interpreter will show an error message. Below is a call to this function with one and no arguments along with their respective error messages

>>> greet("Monica")    # only one argument
TypeError: greet() missing 1 required positional argument: 'msg'

>>> greet()    # no arguments
TypeError: greet() missing 2 required positional arguments: 'name' and 'msg'

Variable Function Arguments

There are other ways to define a function that can take variable number of arguments.

Python Default Arguments
We can provide a default value to an argument by using the assignment operator (=).

def greet(name, msg="Good morning!"):
    """
    This function greets to
    the person with the
    provided message.

    If the message is not provided,
    it defaults to "Good
    morning!"
    """

    print("Hello", name + ', ' + msg)


greet("Kate")
greet("Bruce", "How do you do?")

Output

Hello Kate, Good morning!
Hello Bruce, How do you do?

In this function, the parameter name does not have a default value and is required (mandatory) during a call.

On the other hand, the parameter msg has a default value of "Good morning!". So, it is optional during a call. If a value is provided, it will overwrite the default value.

Any number of arguments in a function can have a default value. But once we have a default argument, all the arguments to its right must also have default values.

This means to say, non-default arguments cannot follow default arguments. For example, if we had defined the function header above as:

def greet(msg = "Good morning!", name):

We would get an error as:

SyntaxError: non-default argument follows default argument

Python Keyword Arguments

When we call a function with some values, these values get assigned to the arguments according to their position.

For example, in the above function greet(), when we called it as greet("Bruce", "How do you do?"), the value "Bruce" gets assigned to the argument name and similarly "How do you do?" to msg.

Python allows functions to be called using keyword arguments. When we call functions in this way, the order (position) of the arguments can be changed. Following calls to the above function are all valid and produce the same result.

# 2 keyword arguments
greet(name = "Bruce",msg = "How do you do?")

# 2 keyword arguments (out of order)
greet(msg = "How do you do?",name = "Bruce") 

1 positional, 1 keyword argument
greet("Bruce", msg = "How do you do?")

We can mix positional arguments with keyword arguments during a function call. But we must keep in mind that keyword arguments must follow positional arguments.

Having a positional argument after keyword arguments will result in errors. For example, the function call as follows:

greet(name="Bruce","How do you do?")

Will result in an error:

SyntaxError: non-keyword arg after keyword arg

Python Arbitrary Arguments

Sometimes, we do not know in advance the number of arguments that will be passed into a function. Python allows us to handle this kind of situation through function calls with an arbitrary number of arguments.

In the function definition, we use an asterisk (*) before the parameter name to denote this kind of argument. Here is an example.

def greet(*names):
    """This function greets all
    the person in the names tuple."""

    # names is a tuple with arguments
    for name in names:
        print("Hello", name)


greet("Monica", "Luke", "Steve", "John")

Output

Hello Monica
Hello Luke
Hello Steve
Hello John

We have called the function with multiple arguments. These arguments get wrapped up into a tuple before being passed into the function. Inside the function, we use a for loop to retrieve all the arguments back.

Python Basics, Pythons 101!

Morris Mulitu — Sat, 24 Jul 2021 17:10:26 +0000

Introduction: What is Python?

Python is a general-purpose, high level, interpreted language with easy syntax and dynamic semantics. The development of python started as a hobby for its creator Guido Van Rossum in 1989. He wanted to make a language that was beautiful to look at and easy for everyone to read. To do this he used indentation instead of curly braces to basically describe the various blocks of code. The language did not receive so much ‘love’ initially because it was slower than other languages at the time. With the rise of machine learning and artificial intelligence, python has come into the spotlight. It makes the tasks much more useful and easy to implement. With the increased computing power available currently, the focus has shifted to increased productivity even if there shall be some extra time taken when python is used.

Why is Python popular?

Python is the best language to learn as a first-time programmer. Its easy syntax and high-level features make it the best. It is the language for everybody.
Python is an open-source language meaning it is free for anybody to use.
Python can be used to make almost anything. Python can be used in GY applications, web applications, mobile applications, server-side coding, artificial intelligence, machine learning and many more. Python always finds a way to do that which you need to be done.
Python has a huge library or modules support. There is a big community that comes together to make the libraries or modules that can be used to obtain any solutions. For example, machine learning algorithms are already available and you can use them to obtain better solutions. You will hence end up having higher productivity and much less coding in this case.

Features of Python

Simplicity. This makes python fun. It makes you think more of your solution rather than the syntax.
Portability. Python code can be shared among different people and devices and its working remains identical holding all other factors constant.
Interpretation. Python is an interpreted language because it goes through an interpreter, which turns the code into the language understood by your computer’s processor. This makes the management of CPU, memory and debugging much simpler.
The huge library support will help you to obtain solutions to your problems easier. You can get started off with data science, web development and others on the go with python.
Object orientation. You may have questions about how developers make apps that are tuned to a specific domain. This is due to the Object-Oriented Programming concepts. Python supports OOP meaning you can model a real-world problem into your code.

Where is Python used in the industry?

Google - Google uses python to provide better search results based on the ranking of websites and much more.
Dropbox-This cloud storage platform uses python in its server and client applications.
Netflix-Netflix uses machine learning with python to cluster users based on their interest in shows and tailor them such that watchers stick around longer.
NSA-NSA uses python for cybersecurity analysis, encryption and decryption.
BitTorrent-It started as a simple python file. Uses python to transfer files in a peer to peer scenario.

Getting Started

First, download the latest version of Python from the download page.Check the documentation and installation manual provided there ans ensure all system requirements are met prior to installation.

Your "Hello World!"

Create a new folder. You might as well name it helloworld

Launch VS code or any other source-code editor of your choice and open the helloworld folder.

Create a new .py file such as helloworld.py

Enter the following line of code;

print('Hello, World!')

The print() is an inbuilt function to display screen messages. In this case, Hello, World! message will be shown.

To execute the helloworld.py file,launch the Command Prompt if on Windows or the Terminal on macOS or Linux. VS code also has an inbuilt one.

Navigate tyo the folder where the .py file is saved and type

python3 helloworld.py

to display

Hello, World!

Now that you have written your first python, welcome to the world of python programming