Python Programming PDF Tutorial

1. Python Introduction 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?  Pyth...

1. Python Introduction 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?  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?  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  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 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!") output Hello, World! 2. Python Getting Started 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 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! 3. 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  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 if 5 > 2: print("Five is greater than two!") Python will give you an error if you skip the indentation: Example Syntax Error: if 5 > 2: print("Five is greater than two!") The number of spaces is up to you as a programmer, the most common use is four, but it has to be at least one. 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 Syntax Error: if 5 > 2: print("Five is greater than two!") print("Five is greater than two!")  Comments Python has commenting capability for the purpose of in-code documentation. Comments start with a #, and Python will render the rest of the line as a comment: Example Comments in Python: #This is a comment. print("Hello, World!") 4. Python Variables In Python, variables are created when you assign a value to it: Example Variables in Python: x=5 y = "Hello, World!" Python has no command for declaring a variable. Variables are containers for storing data values. 4.1 Creating Variables Python has no command for declaring a variable. A variable is created the moment you first assign a value to it. Example x=5 y = "John" print(x) print(y) Variables do not need to be declared with any particular type, and can even change type after they have been set. Example x = 4 # x is of type int x = "Sally" # x is now of type str print(x) Casting If you want to specify the data type of a variable, this can be done with casting. Example x = str(3) # x will be '3' y = int(3) # y will be 3 z = float(3) # z will be 3.0 Get the Type You can get the data type of a variable with the type() function. Example x=5 y = "John" print(type(x)) print(type(y) Single or Double Quotes? String variables can be declared either by using single or double quotes: Example x = "John" # is the same as x = 'John' Case-Sensitive Variable names are case-sensitive. Example This will create two variables: a=4 A = "Sally" #A will not overwrite a 4.2 Python - Variable Names Variable Names A variable can have a short name (like x and y) or a more descriptive name (age, carname, total_volume). Rules for Python variables:  A variable name must start with a letter or the underscore character  A variable name cannot start with a number  A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )  Variable names are case-sensitive (age, Age and AGE are three different variables)  A variable name cannot be any of the Python keywords. Example Legal variable names: myvar = "John" my_var = "John" _my_var = "John" myVar = "John" MYVAR = "John" myvar2 = "John" Example Illegal variable names: 2myvar = "John" my-var = "John" my var = "John" Remember that variable names are case-sensitive Multi Words Variable Names Variable names with more than one word can be difficult to read. There are several techniques you can use to make them more readable: Camel Case Each word, except the first, starts with a capital letter: myVariableName = "John" Pascal Case Each word starts with a capital letter: MyVariableName = "John" Snake Case Each word is separated by an underscore character: my_variable_name = "John"