Workshop: Introduction to programming (with Python)
Welcome to Introduction to Programming!
Setting up your work station
- Download Python - You can download it here
- Check that your installation was successful - We will do this by checking the version of python we just downloaded. We can do this by opening up our command prompt and simply typing "python --version". If you did everything right you should see a message that looks something like this: "Python 3.7.3"
- Let's test our distribution - Let's get our first introduction into Python programming by making a hello world file.
Basic Hello World Program
A hello world program is the most basic program you can write to test that your distribution is working smoothly.
- Open a text editor - This is where we will be writing all of our code. There are many different editors you can use, so feel free to choose the one you are most comfortable with. The only requirement is that the text editor should be able to product plain text files. Windows users already have Notepad installed. Mac users have TextEdit (other text editors include TextWrangler, Atom, and much more).
- Write your code - To make this program as simple as possible we will simply write a print statement. After writing your print statement save the file to your Desktop (or whatever other directory you want) as "hello.py". All python files need to have the extension .py
- Execute the code - Now is the fun part, running the code! Open up the command prompt (Terminal for Mac Users, Powershell for Windows). Navigate to the directory where you saved the file (ex: cd Desktop). Now execute your python code by typing "python [filename]"
Now that we understand the basic workflow of python (create code in text editor → execute in command prompt), we can start discussing the different functions and capabilities of Python. We can start this discussion with variables. You can think of variables as the objects that store information for our program. A variable has two basic parts; A name (which we will use to refer to the variable) and A value (the info we care about). Besides those two parts, variables can hold different types of information.
Types Of Variables:
- Strings - A sequence of characters (ex: "Python is fun!")
- Integers - Whole numbers (ex: 3, 10, 999)
- Floats - Numbers w/ a decimal (ex: 1.0, 3.14, 7.77)
- Lists - An sequential list of other variables (floats, integers, strings, more lists, or a mix) (ex: ['cat', 'dog', 999, 3.14, variable1])
One of the great features of Python is that the built in compiler can intelligently figure out what type of variable your specified variables should be and takes care of this distinction automatically. This means defining variables is easier in Python than some other languages you may be familiar with. We define a variable by writing its name, followed by an equal sign, followed by the value of the variable (ex: pi=3.14, name="Dylan", eq="3+4"). We can also define variables without setting the values immediately. To do this we need to tell the compiler what type of variable we need (since it can't figure it out automatically) (ex: int pi, str myName)
Important Note: The standard naming convention of variables follows: The first word is always all lowercase then the proceeding words begin with an uppercase letter (ex: myVariable, reallyAwesomeInteger). You don't need to follow this convention, but it is worth knowing.
To update a variable (change it's value later on in the code) we simply need to redefine it's value. You can do this by:
variableName = [new value]
When we get into more complex implementations our variable type will become very important. Ask yourself 'what is the difference between these two codes?'
- float sum = 1.5 + 3
- int sum = 1.5 + 3
Answer: 1.5 + 3 = 4.5 but 4.5 is a float value. So for code #1 the answer is 4.5, but the "sum" variable in code #2 is an integer so the answer will be rounded down to 4.
It because of cases like these that sometimes we implement a technique known as casting. Casting simply means changing the type of information a variable holds. With casting we can turn a int to a float, float to an int, str to an int, etc. We cast by writing the variable type we want ("float", "int", "str", etc.) followed by the variable/value we want to cast enclosed by parenthesis.
- float(3) → 3.0
- int(2.9999) → 2
- int("1964") → 1964