In this article, we will cover python basics. We will discuss what is python, where you can download python from, the basic syntax of python, how to input and output information in and out of your python scripts, how to do loops, conditional operators (if/else/elif), and how to write basic functions.
What is Python?
Python is a cross platform interpreted programming language that was introduced in 1989. The great thing about Python is that it is cross platform. You can run your basic Python applications on any platform that you can install the Python runtime environment. This somewhat fills the need that Java programming was meant to solve. An Object Oriented Cross-Platform programming language.
Installing Python
In this section we will discuss how to install python for each of the major platforms. There are 3 versions of Python:
- Python
- Python 2
- Python 3
No one really uses the first version of Python anymore. The most common version is Python 2. And most development is now around Python 3. For that reason, I would recommend you focus on Python 3 instead of python 2. However, for the purposes of this article, either one will work for you.
Ubuntu
Run the following command from a terminal window to install Python 2.x:
apt-get update
sudo apt-get install python
Run the following commands from a terminal window to install Python 3.x:
sudo apt-get update
sudo apt-get install python3
OSX/MacOS
If you want Python 2.x, you are in luck. Python 2.7 ships on OSX. That said, Python 2.7 is only supported until 2020. Given that, I recommend you switch to Python 3.x, it is easy enough to install.
If you have homebrew installed, you simply run:
brew install python3
If you do not have homebrew installed, I would recommend you install homebrew as it will make your life much easier.
Windows
If you are on windows, you can download the latest builds from the official Python website. Simply download the appropriate build for your version of windows and you can select whether you want to download python 2.x or 3.x. After it is downloaded, double-click on the installer, click through the installation wizard, and you will have python installed.
If you are using Chocolatey, my favorite way to install programs, you can install the latest version of python 3 by running:
choco install python
Installing Pip
Pip is a package manager for python, and I would highly recommend that you install pip at this stage. Once you have the basics of python down, there are a lot of modules that extend Python's functionality. Pip allows you to easily install these modules and then use them as you write your python scripts/applications.
To install pip, you have a few options. You can download the get-pip script, then run:
python get-pip.py
Alternatively, if you are running on OSX and you have homebrew installed, you can run:
brew install pip
Or, on OSX or Linux, you can install pip with this one line command:
curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py
Finally, if you are on Windows, Linux, or MacOS, you can install using easy install, an alternative package manager for Python. To install using easy install, just run:
easy_install pip
Basic Python Programming
Now that you have Python installed, you can start writing scripts. Here are a few things you might find useful.
Syntax
In some languages, you use the concept of curly braces for defining what code goes together. For example, in C syntax, you might create an if statement that looks something like this:
if(a>b){do something;}
In the above example, you see that I have put in an opening and closing curly brace around "do something". This is how I define the blocks of code. If what I put in the parentheses is true, it runs whatever is in the curly braces.
Python is different in that there are no curly braces for code blocks. Rather, Python uses indentation to define blocks of code. This forces you to create more readable code. And it also means you no longer have to spend hours troubleshooting your un-balanced curly braces. Here is an example of some python code:
if a > b:
do something
The above code does the same thing as my C syntax example. If A is greater than B, then it will do something. However, I did not use any curly braces. Rather, I indented the second line to tell the python interpreter that "do something" was in the code block for the if statement.
Input
There are a few ways to input into your python script. You can input via the console. You can input via a file. To prompt for user input, you would run the following:
name = input("What is your name?")
The above code will prompt the user to enter their name, and save whatever they type into the name variable.
Next lets look at how to read in a file:
myfile = open('myfile.txt','r')
text = myfile.read()
The above code declares a file variable called myfile. We then populate the text variable by using the read function attached to the myfile object. The result is we have read the contents of myfile.txt into the text variable.
Output
In the previous section we discussed how to input into your python script via the console and by reading in a file. Next we will look at how we can output from our python script.
First, how do we output to the console? That one is easy.
print("hello world")
Or, if we want to use the example from the previous section, we can read in the first line from a text file, and then print it to the console:
myfile = open('myfile.txt','r')
text = myfile.readline()
print(text)
Next, lets read in something from the console, and write it to a file. There are two ways we can write to a file. We can write in a manner that we overwrite the existing file. Or, we can simply append to the existing file.
In this example, we will overwrite an existing file:
name = input("What is your name?")
myfile = open('myfile.txt','w')
myfile.write(name)
myfile.close()
In this example we will append to an existing file:
name = input("What is your name?")
myfile = open('myfile.txt','a')
myfile.write(name)
myfile.close()
The only difference between the two examples above is the second argument I passed. To write to a file, I pass a 'w', to append to a file, I passed an 'a'. And in the previous examples, I passed an 'r' to open the file as read only.
If/Else/Elif
The most common logic operators are else, if, and else if. Lets start with an example:
x = 10
if x < 5:
print("less than 5")
elif x > 15:
print("Greater than 15")
else:
print("greater than 5, less than 15")
The above example demonstrates all three operators I mentioned. First we declared the variable x and set the value to 10. We then checked to see if it was less than 5 using the if statement. If it was less than 5, we would have printed the text "less than 5".
Next, we used the elif operator to do a second check. If x was greater than 15, it would have printed "Greater than 15" to the console.
Finally we used the else operator. This is the default state if none of the other conditions are true. In this case it printed "greater than 5, less than 15" because none of the other two conditions were met.
Loops
Loops are important as they allow you to run the same block of code many times without having to re-type the same code over and over again. There are two main kinds of loops:
- For loops
- While loops
The difference being with for loops you declare all the variables at the time that you declare the loop. With while loops you declare the variables separately. Lets start with a for loop:
myfile = open('myfile.txt','r')
for line in myfile:
print(line)
The above loop declares the line variable, then prints each line in myfile. In this case, myfile is a collection of lines from myfile.txt.
Next we will look at a while loop. Let's say we want to run a block of code 10 times:
x=0
while x < 10:
print("hello")
x = x + 1
The above code will print the word "hello" 10 times. Each iteration it will increment the value of x by one. Once x reaches 10, it is no longer less than 10 and it will break out of the loop.
Functions
Functions allow you to group bits of code together that you wish to call many times. It lets you have cleaner code, fewer errors, and fewer headaches. First, lets declare our first function:
def myfunction():
print("hello")
print("hello")
print("hello")
The above code declares a function called myfunction. All the function does is print the word "hello" three times on the console. When we want to call the function, we just have to type:
myfunction()
Each time you type the above function name, it will print "hello" three times.
Next, lets look at passing variables to a function:
def myfunction(name):
print("hello " + name)
print("hello "+ name)
print("hello "+ name)
In the above function, we declared a variable of name. When the function is called, it will print hello followed by the name you passed to the function. To call the function now, you must pass a variable to it:
myfunction("bob")
I hope this article on python basics has been helpful. We have covered how to input and output information in and out of your python scripts, how to do loops, conditional operators of if/else/elif, and how to write basic functions.
