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INTRODUCTION
What is Python?
What is Python?
Python is a popular programming language. It was created by Guido van Rossum, and released in 1991.
It is used for:
web development (server-side),
software development,
mathematics,
system scripting.
What can Python do?
What can Python do?
Python can be used on a server to create web applications.
Python can be used alongside software to create workflows.
Python can connect to database systems. It can also read and modify files.
Python can be used to handle big data and perform complex mathematics.
Python can be used for rapid prototyping, or for production-ready software development.
Why Python?
Why Python?
Python works on different platforms (Windows, Mac, Linux, Raspberry Pi, etc).
Python has a simple syntax similar to the English language.
Python has syntax that allows developers to write programs with fewer lines than some other programming languages.
Python runs on an interpreter system, meaning that code can be executed as soon as it is written. This means that prototyping can be very quick.
Python can be treated in a procedural way, an object-oriented way or a functional way.
Good to know
Good to know
The most recent major version of Python is Python 3, which we shall be using in this tutorial. However, Python 2, although not being updated with anything other than security updates, is still quite popular.
In this tutorial Python will be written in a text editor. It is possible to write Python in an Integrated Development Environment, such as Thonny, Pycharm, Netbeans or Eclipse which are particularly useful when managing larger collections of Python files.
Python Syntax compared to other programming languages
Python Syntax compared to other programming languages
Python was designed for readability, and has some similarities to the English language with influence from mathematics.
Python uses new lines to complete a command, as opposed to other programming languages which often use semicolons or parentheses.
Python relies on indentation, using whitespace, to define scope; such as the scope of loops, functions and classes. Other programming languages often use curly-brackets for this purpose.
EXAMPLE :
print("Hello, World!")
GET STARTED
Python Install
Python Install
Many PCs and Macs will have python already installed.
To check if you have python installed on a Windows PC, search in the start bar for Python or run the following on the Command Line (cmd.exe):
C:\Users\Your Name>python --version
To check if you have python installed on a Linux or Mac, then on linux open the command line or on Mac open the Terminal and type:
python --version
If you find that you do not have python installed on your computer, then you can download it for free from the following website: https://www.python.org/
Python Quickstart
Python Quickstart
Python is an interpreted programming language, this means that as a developer you write Python (.py) files in a text editor and then put those files into the python interpreter to be executed.
The way to run a python file is like this on the command line:
C:\Users\Your Name>python helloworld.py
Where "helloworld.py" is the name of your python file.
Let's write our first Python file, called helloworld.py, which can be done in any text editor.
helloworld.py
print("Hello, World!")
Simple as that. Save your file. Open your command line, navigate to the directory where you saved your file, and run:
C:\Users\Your Name>python helloworld.py
The output should read:
Hello, World!
Congratulations, you have written and executed your first Python program.
The Python Command Line
The Python Command Line
To test a short amount of code in python sometimes it is quickest and easiest not to write the code in a file. This is made possible because Python can be run as a command line itself.
Type the following on the Windows, Mac or Linux command line:
C:\Users\Your Name>python
Or, if the "python" command did not work, you can try "py":
C:\Users\Your Name>py
From there you can write any python, including our hello world example from earlier in the tutorial:
C:\Users\Your Name>python
Python 3.6.4 (v3.6.4:d48eceb, Dec 19 2017, 06:04:45) [MSC v.1900 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> print("Hello, World!")
Which will write "Hello, World!" in the command line:
C:\Users\Your Name>python
Python 3.6.4 (v3.6.4:d48eceb, Dec 19 2017, 06:04:45) [MSC v.1900 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> print("Hello, World!")
Hello, World!
Whenever you are done in the python command line, you can simply type the following to quit the python command line interface:
exit()
SYNTAX
Execute Python Syntax
Execute Python Syntax
As we learned in the previous page, Python syntax can be executed by writing directly in the Command Line:
>>> print("Hello, World!")
Hello, World!
Or by creating a python file on the server, using the .py file extension, and running it in the Command Line:
C:\Users\Your Name>python myfile.py
Python Indentation
Python Indentation
Indentation refers to the spaces at the beginning of a code line.
Where in other programming languages the indentation in code is for readability only, the indentation in Python is very important.
Python uses indentation to indicate a block of code.
Example
Example
if 5 > 2:
print("Five is greater than two!")
Python will give you an error if you skip the indentation:
Example
Example
Syntax Error:
if 5 > 2:
print("Five is greater than two!")
The number of spaces is up to you as a programmer, but it has to be at least one.
Example
Example
if 5 > 2:
print("Five is greater than two!")
if 5 > 2:
print("Five is greater than two!")
You have to use the same number of spaces in the same block of code, otherwise Python will give you an error:
Example
Example
Syntax Error:
if 5 > 2:
print("Five is greater than two!")
print("Five is greater than two!")
COMMENTS
Comments can be used to explain Python code.
Comments can be used to make the code more readable.
Comments can be used to prevent execution when testing code.
Creating a Comment
Creating a Comment
Comments starts with a #, and Python will ignore them:
Example
Example
#This is a comment
print("Hello, World!")
Comments can be placed at the end of a line, and Python will ignore the rest of the line:
Example
Example
print("Hello, World!") #This is a comment
A comment does not have to be text that explains the code, it can also be used to prevent Python from executing code:
Example
Example
#print("Hello, World!")
print("Cheers, Mate!")
Multi Line Comments
Multi Line Comments
Python does not really have a syntax for multi line comments.
To add a multiline comment you could insert a # for each line:
Example
Example
#This is a comment
#written in
#more than just one line
print("Hello, World!")
Or, not quite as intended, you can use a multiline string.
Since Python will ignore string literals that are not assigned to a variable, you can add a multiline string (triple quotes) in your code, and place your comment inside it:
Example
Example
"""
This is a comment
written in
more than just one line
"""
print("Hello, World!")
As long as the string is not assigned to a variable, Python will read the code, but then ignore it, and you have made a multiline comment.
USER INPUT
User Input
User Input
Python allows for user input.
That means we are able to ask the user for input.
The method is a bit different in Python 3.6 than Python 2.7.
Python 3.6 uses the input() method.
Python 2.7 uses the raw_input() method.
The following example asks for the username, and when you entered the username, it gets printed on the screen:
Python 3.6
Python 3.6
username = input("Enter username:")
print("Username is: " + username)
Python 2.7
Python 2.7
username = raw_input("Enter username:")
print("Username is: " + username)
Python stops executing when it comes to the input() function, and continues when the user has given some input.
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