7 reasons to learn Python

Python is described as an interpreted and dynamic programming language with a focus on code readability. Have fewer steps to coding than Java or C++.

Why Python is Awesome

It can be used for the programming of the front end (client side) with which users interact and back end (server side) database of your website. It can be used for numerical and data analysis for scientific study and research. It can be used to develop artificial intelligence. It can be used to develop both online and offline applications from productivity tools, games and other type of app you can think off.

Getting started

To run Python programs, you will need the Python interpreter and possibly a graphical editor. A Python interpreter executes Python code (sometimes called programs). You can download the Python interpreter here: https://www.python.org/downloads/ Once you have a Python interpreter installed, continue with this tutorial. To run the code, open a terminal and launch:

python file.py

Python IDE

An IDE is a development environment. If you don’t want to work from the terminal, you can use an IDE. This is a graphical editor in which you can type code, work with multiple files, run code amongst other things.

Execute Python scripts

Execute Python scripts in the terminal or an IDE. Python files have the .py extension. Whenever you make a Python script, save it as name.py A simple program (hello.py) is shown below. The first line indicates that we want to use the Python interpreter. The 3rd line outputs a line of text “hello wlrd” to the screen. The text below can be copied into a text editor and save as hello.py. Python works with files that end in .py.

#!/usr/bin/env python3 print('hello world')

Python supports different types of variables (datatypes) such as whole numbers, floating point numbers and text. You do not need to specify the datatype of a variable, you can simply assign any value to a variable. Type the program below and start it. The example below shows you several variables. These can be assigned as you wish. Once defined you can print them or use arithmetics.

#!/usr/bin/python x = 3 # a whole number f = 3.1415926 # a floating point number name = "Python" # a string print(x) print(f) print(name) combination = name + " " + name print(combination) sum = f + f print(sum)

Any time you want to use text in Python, you are using strings. Python understands you want to use a string if you use the double-quotes symbol. Once a string is created, you can simply print the string variable directly. You can access characters using block quotes.

Variables can be of the string data type. They can hold characters or text. If you create string variable x. You can show it on the screen using the print() function.

x = "Hello" print(x)

Python has builtin support for string replacement. A string is a variable that contains text data. Can call the string.replace(old, new) method using the string object. This article demonstrates the replace method. Try the program below:

s = "Hello World" s = s.replace("World","Universe") print(s)

The join(sequence) method joins elements and returns the combined string. The join methods combines every element of the sequence. The join method takes a sequence as argument. The sequence is written as single argument: you need to add brackets around the sequence. If you’d like, you can pass a variable holding the sequence as argument. This makes it easier to read. We’ll use a space a seperator string in the example below. Try the program below:

# define strings firstname = "Bugs" lastname = "Bunny" # define our sequence sequence = (firstname,lastname) # join into new string name = " ".join(sequence) print(name)

A string can be split into substrings using the split(param) method. This method is part of the string object. The parameter is optional, but you can split on a specific string or character. If you have a string, you can subdivide it into several strings. The string needs to have at least one separating character, which may be a space. By default the split method will use space as separator. Calling the method will return a list of all the substrings.

s = "Its to easy" words = s.split() print(words)
Keyboard input

In Python and many other programming languages you can get user input. Do not worry, you do not need to write a keyboard driver. The input() function will ask keyboard input from the user. If you are still using Python 2, you have the function raw_input(). The input function prompts text if a parameter is given. The functions reads input from the keyboard, converts it to a string and removes the newline (Enter). Type and experiment with the script below (save as key.py)

#!/usr/bin/env python3 name = input('What is your name? ') print('Hello ' + name) job = input('What is your job? ') print('Your job is ' + job) num = input('Give me a number? ') print('You said: ' + str(num))
For Loops

Programs sometimes need to repeat actions. To repeat actions we can use a for loop. A for loop is written inside the code. A for loop can have 1 or more instructions. A for loop will repeat a code block. Repeation is continued until the stop condition is met. If the stop condition is not met it will loop infintely. These instructions (loop) is repeated until a condition is met.

#!/usr/bin/env python3 city = ['Tokyo','New York','Toronto','Hong Kong'] print('Cities loop:') for x in city: print('City: ' + x) print('\n') # newline num = [1,2,3,4,5,6,7,8,9] print('x^2 loop:') for x in num: y = x * x print(str(x) + '*' + str(x) + '=' + str(y))

To group sets of code you can use functions. Functions are small parts of repeatable code. A function accepts parameters. Without functions we only have a long list of instructions. Functions can help you organize code. Functions can also be reused, often they are included in modules. Functions can be seen as executable code blocks. A function can be used once or more. A simple example of a function is:

def currentYear(): print('2018') currentYear()

List can be seen as a collection: they can hold many variables. List resemble physical lists, they can contain a number of items. A list can have any number of elements. They are similar to arrays in other programming languages. Lists can hold all kinds of variables: integers (whole numbers), floats, characters, texts and many more.

list = [] ratings = [ 3,4,6,3,4,6,5 ]
List operations

To add items to a list, you can use the append() method. Call the method on the list, the parameter contains the item to add. Calling append(3) would add 3 to the list. To remove an item from the end of the list, you can use the pop() method.

x = [3,4,5] x.append(6) print(x) x.append(7) print(x) x.pop() print(x)
Read file

Reading files is part of the Python standard library. This means you do not have to include any module. There are two ways to read files: line by line read block

Line by line

#!/usr/bin/env python filename = "file.py" with open(filename) as f: content = f.readlines() print(content)

Read block

#!/usr/bin/env python filename = "file.py" infile = open(filename, 'r') data = infile.read() infile.close() print(data)
Write file

Write file functionality is part of the standard module, you don’t need to include any modules. Writing files and appending to a file are different in the Python language. You can open a file for writing using the line

f = open("test.txt","w")

to append to a file use:

f = open("test.txt","a")

Variables have a certain reach within a program. A global variable can be used anywhere in a program, but a local variable is known only in a certain area (function, loop) Sometimes the word scope is used in projects: “its outside the scope of the project”, meaning not included. Likewise, a variable can be outside the scope of a function. Scope has to do with where a variable can be used. If you define a variable, it’s not necessarily usable everywhere in the code. A variable defined in a function is only known in a function, unless you return it.

def something(): localVar = 1 # this will crash because localVar is a local variable print(localVar)

In the program below, balance is a global variable. It can be used anywhere in the code. But the variable x can only be used inside addAmount.

#!/usr/bin/env python3 balance = 0 def addAmount(x): global balance balance = balance + x addAmount(5) print(balance)
Try exception

The try except statement can handle exceptions. Exceptions may happen when you run a program. Exceptions are errors that happen during execution of the program. Python won’t tell you about errors like syntax errors (grammar faults), instead it will abruptly stop. An abrupt exit is bad for both the end user and developer. Instead of an emergency halt, you can use a try except statement to properly deal with the problem. An emergency halt will happen if you do not properly handle exceptions.

try: 1 / 0 except ZeroDivisionError: print('Divided by zero') print('Should reach here')

Python class is concept of “object oriented programming”. Python is an object oriented programming language (oop). OOP is a way to build software. With OOP you can make your program much more organized, scalable, reusable and extensible. The OOP concept can be a bit weird. It can be challenging to grasp, but it’s a very powerful concept. Lets create a theoritcal example, we create an object dog. Creating an object is just one line of code:

obj1 = dog()

Each object can have variables. The values of those variables are unique to the object. We set object variables (name,age)

obj1.name = "Woof" obj1.age = 5

If methods exist for an object, they can be called. The objects unique variables can be used in those methods. The methods can be used multiple times:

obj1.bark() obj1.bark()

The constructor is a method that is called when an object is created. This method is defined in the class and can be used to initialize basic variables. If you create four objects, the class constructor is called four times. Every class has a constructor, but its not required to explicitly define it. Inside the constructor we initialize two variables: legs and arms. Sometimes variables are named properties in the context of object oriented programming. We create one object (bob) and just by creating it, its variables are initialized.

class Human: def __init__(self): self.legs = 2 self.arms = 2 bob = Human() print(bob.legs)

Modules can have one or more functions. They help you to organize your code. Instead of one long Python file, you can have several files (modules). A module is a Python file that has functions or classes. A Python program can use one or more modules. You can load a module with the import keyword. In the example below we load the os module. This is short for operating system, so you can do system tasks.

import os os.system("dir")

Inheritance: A class can get the properties and variables of another class. This class is called the super class or parent class. Inheritances saves you from repeating yourself (in coding: dont repeat yourself), you can define methods once and use them in one or more subclasses. First we define the super class. The super class is written just like a normal class, there’s nothing special about it except that others will inherit from it. You can give it methods and variables if you want.

class App: def start(self): print('starting')
Class method

A class method is a method that’s shared among all objects. To call a class method, put the class as the first argument. Class methods can be can be called from instances and from the class itself. All of these use the same method. The method can use the classes variables and methods. The example below defines a class method. The class method can then be used by the class itself. In this example the class method uses the class property name.

class Fruit: name = 'Fruitas' @classmethod def printName(cls): print('The name is:', cls.name) Fruit.printName()

You can use a classmethod with both objects and the class:

apple = Fruit() berry = Fruit() Fruit.printName() apple.printName() berry.printName()

The parameter name now belongs to the class, if you’d change the name by using an object it ignores that. But if you’d do that by the class it changes, example below:

apple.name="Apple" Fruit.printName() apple.printName() berry.printName() Fruit.name="Apple" Fruit.printName() apple.printName() berry.printName()

All the documentation in this page is taken from Python Basics