Modules and Imports

A module is a Python file that can hold reusable code.

If a file named stats_tools.py contains:

sum(values) adds the numeric items. It is the built-in form of the running total loop from Chapter 3.

another file can import it:

That is the basic idea: move reusable functions out of one script and import them where they are needed.

Imports make names available

This import:

from pathlib import Path

makes the name Path available in the current file.

This import:

import math

makes the module name math available:

print(math.sqrt(9))

The two styles create different names:

Prefer clear imports

For this course, avoid imports that hide where a name came from:

from math import *

That form fills the current file with many names. It is convenient for quick experiments, but it makes code harder to read.

A module should not surprise the importer

When a module is imported, Python runs the top-level code in that module. That means a module should usually define functions and constants at top level, not run a whole program immediately.

Good module shape:

Risky module shape:

Importing the second file would try to read input.txt immediately.

import math