When the computer runs code in a file, it will read the file and execute instructions in order. It will start from the top, execute that line of code and move onto the next line.

The order is very important. The code will produce different results if the order is changed. Try swapping lines 2 and 3 and see if the output changes.

In this course and in general while coding, we will use lines numbers to keep track of which line of code the computer is currently executing.

We don't write them in our code, as the computer will not understand them, but many programs used to read and write code will draw them to left hand side of the code. This helps us keep track of where we are and helps us discuss the code with each other.

For example, if I say "there's a typo in your print instruction", it wouldn't be clear which print statement. Instead, I would say "there's a typo on line 3"

Also, when there's an error, Python will use the line number to tell you where the error is. Try running and fixing this code.

Normally, when we are coding we write instructions in a python file and ask the computer to run it. This course is a bit different, it can run the code in your browser so you don't have to install Python.

For now, you can pretend what is in the code blocks are the contents of a file. The course will cover running Python from a file later.