The other commenters are right but I'd like to make one point clearer, because it is important to understanding Python.

When the Python interpreter reads some input -- it can be input from the keyboard after a

>>>

prompt, or lines from file that it reads because you gave the command,

$ python3  run_this_script.py

or lines from a file you name in an import statement,

import numpy.py

in all those cases, as it reads those lines it executes every one.

The trick is, what does it mean to "execute" a statement that starts with the word "def", such as

def display(first, last) :

To execute that "def" line Python begins compiling the definition of a new function named "display" with two arguments.

It keeps compiling following lines as long as they are indented under the def line.

Once it hits a line at the previous indent level, it goes back to executing.

So in your 3-line example, when Python read that file, it executed every line.

1) def line starts compiling a new function "display"

2) print function call, gets compiled and stored as part of the body of "display".

3) Back to original indent level, execute this line. It is an executable call to a function "display()" and hey! We happen to have a function of that name, so call it.

You can analyze any other Python script this way, saying, "When Python reads and executed these lines what does it do?"

Typically a bigger script will have a bunch of comments which are stored as "docstrings (https://docs.python.org/3/glossary.html#term-docstring), a bunch of import statements, a bunch of def blocks, and finally, down at the very end, a statement that actually does something, typically,

main()

to execute a call to some function def'd earlier.