Sheridan Chris. - Learn Python In a Weekend, Python for Beginners

Before we can write our first Python program , we have to download the appropriate interpreter for our computers .

We ll be using Python in this book because as stated on the official Python site Python x is legacy , Python x is the present and future of the language . In addition , Python eliminates many quirks that can unnecessarily trip up beginning programmers .

However , note that Python is currently still rather widely used . Python and are about 90% similar . Hence if you learn Python 3, you will likely have no problems understanding codes written in Python

To install the interpreter for Python 3, head over to https :// www . python . org / downloads /. The correct version should be indicated at the top of the webpage . Click on the version for Python and the software will start downloading .

Alternatively if you want to install a different version , scroll down the page and you ll see a listing of other versions . Click on the release version that you want . We ll be using version 3.4.2 in this book . You ll be redirected to the download page for that version .

Scroll down towards the end of the page and you ll see a table listing various installers for that version . Choose the correct installer for your computer . The installer to use depends on two factors :

The operating system ( Windows , Mac OS , or Linux ) and The processor (32- bit vs 64- bit ) that you are using .

For instance , if you are using a 64- bit Windows computer , you will likely be using the " Windows x 86-64 MSI installer ". Just click on the link to download it . If you download and run the wrong installer , no worries . You will get an error message and the interpreter will not install . Simply download the correct installer and you are good to go .

Once you have successfully installed the interpreter , you are ready to start coding in Python .

Using the Python Shell , IDLE and Writing our FIRST program

We ll be writing our code using the IDLE program that comes bundled with our Python interpreter .

To do that , let s first launch the IDLE program . You launch the IDLE program like how you launch any other programs . For instance on Windows 8, you can search for it by typing IDLE in the search box . Once it is found , click on IDLE ( Python GUI ) to launch it . You ll be presented with the Python Shell shown below .

The Python Shell allows us to use Python in interactive mode . This means we can enter one command at a time . The Shell waits for a command from the user , executes it and returns the result of the execution . After this , the Shell waits for the next command .

Try typing the following into the Shell . The lines starting with >>> are the commands you should type while the lines after the commands show the results .

>>> 2+3 5 >>> 3>2 True >>> print ( Hello World ) Hello World

When you type 2+3, you are issuing a command to the Shell , asking it to evaluate the value of 2+3. Hence , the Shell returns the answer When you type 3>2, you are asking the Shell if is greater than The Shell replies True . Finally , print is a command asking the Shell to display the line Hello World .

The Python Shell is a very convenient tool for testing Python commands , especially when we are first getting started with the language . However , if you exit from the Python Shell and enter it again , all the commands you type will be gone . In addition , you cannot use the Python Shell to create an actual program . To code an actual program , you need to write your code in a text file and save it with a . py extension . This file is known as a Python script .

To create a Python script , click on File > New File in the top menu of our Python Shell . This will bring up the text editor that we are going to use to write our very first program , the Hello World program . Writing the Hello World program is kind of like the rite of passage for all new programmers . We ll be using this program to familiarize ourselves with the IDLE software .