Learn Python quick. Jens Braun
2: mathGame.py
Appendix A: Working With Strings
Appendix B: Working With Lists
Appendix C: Working With Tuples
Appendix D: Working With Dictionaries
Chapter 1: Python, what Python?
Welcome to the exciting world of programming. I'm so glad you picked up this book and I sincerely hope this book can help you master the Python language and experience the exhilaration of programming. Before we dive into the nuts and bolts of Python programming, let us first answer a few questions.
What is Python?
Python is a widely used high-level programming language created by Guido van Rossum in the late 1980s. The language places strong emphasis on code readability and simplicity, making it possible for programmers to develop applications rapidly.
Like all high level programming languages, Python code resembles the English language which computers are unable to understand. Codes that we write in Python have to be interpreted by a special program known as the Python interpreter, which we’ll have to install before we can code, test and execute our Python programs. We'll look at how to install the Python interpreter in Chapter 2.
There are also a number of third-party tools, such as Py2exe or Pyinstaller that allow us to package our Python code into stand-alone executable programs for some of the most popular operating systems like Windows and Mac OS. This allows us to distribute our Python programs without requiring the users to install the Python interpreter.
Why Learn Python?
There are a large number of high level programming languages available, such as C, C++, and Java. The good news is all high level programming languages are very similar to one another. What differs is mainly the syntax, the libraries available and the way we access those libraries. A library is simply a collection of resources and pre-written codes that we can use when we write our programs. If you learn one language well, you can easily learn a new language in a fraction of the time it took you to learn the first language.
If you are new to programming, Python is a great place to start. One of the key features of Python is its simplicity, making it the ideal language for beginners to learn. Most programs in Python require considerably fewer lines of code to perform the same task compared to other languages such as C. This leads to fewer programming errors and reduces the development time needed. In addition, Python comes with an extensive collection of third party resources that extend the capabilities of the language. As such, Python can be used for a large variety of tasks, such as for desktop applications, database applications, network programming, game programming and even mobile development. Last but not least, Python is a cross platform language, which means that code written for one operating system, such as Windows, will work well on Mac OS or Linux without making any changes to the Python code.
Convinced that Python is THE language to learn? Let’s get started...
Chapter 2: Getting ready for Python
Installing the Interpreter
Before we can write our first Python program, we have to download the appropriate interpreter for our computers.
We’ll be using Python 3 in this book because as stated on the official Python site “Python 2.x is legacy, Python 3.x is the present and future of the language”. In addition, “Python 3 eliminates many quirks that can unnecessarily trip up beginning programmers”.
However, note that Python 2 is currently still rather widely used. Python 2 and 3 are about 90% similar. Hence if you learn Python 3, you will likely have no problems understanding codes written in Python 2.
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 3 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:
1. The operating system (Windows, Mac OS, or Linux) and
2. 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 x86-64 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 5. When you type 3>2, you are asking the Shell if 3 is greater than 2. The Shell replies True. Finally, print is a command asking the Shell to display the line Hello World.
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