Importing Modules: import Statement

Organizing code into separate files (modules) is a beneficial practice. To use code from one file inside another, Python provides the import statement. This statement is the fundamental mechanism for loading and using code defined in other modules.

The Basic import Statement

The simplest way to use a module is with the import keyword followed by the name of the module file (without the .py extension).

Let's say you want to use some mathematical functions. Python comes with a built-in module named math that contains many useful mathematical operations and constants. To use it, you start your script with:

import math

What does this line actually do?

1. Finds the Module: Python searches for a file named math.py (or other types of modules, but primarily .py files for now) in a specific list of directories it knows about. This list includes the directory containing your current script and standard library locations.
2. Executes the Module (if needed): If the module hasn't been loaded before in the current program execution, Python runs the code inside math.py. This makes all the functions, variables, and classes defined in math.py available.
3. Creates a Namespace: This is a very important point. The import math statement does not directly copy all the functions like sqrt or constants like pi from the math module into your current script's main workspace. Instead, it creates a single name in your script's namespace: math. This math name now refers to the module object itself.

Accessing Module Contents: Dot Notation

Because import math creates a namespace called math, you need to tell Python where to look for the functions or variables defined within that module. You do this using dot notation: module_name.item_name.

To use the square root function (sqrt) from the math module, you would write:

math.sqrt(16)

To access the constant pi (pi), you would write:

math.pi

This explicit module_name. prefix is beneficial because it prevents naming conflicts. If you had defined your own variable named pi in your script, it wouldn't clash with math.pi because they exist in different namespaces. Your pi is in the main script's namespace, while the mathematical constant is accessed through the math namespace.

Example: Using the math Module

Here's a complete, simple script demonstrating the import and usage:

# Import the entire math module
import math

# Calculate the square root of 25
number = 25
square_root = math.sqrt(number)
print(f"The square root of {number} is {square_root}") # Output: The square root of 25 is 5.0

# Calculate the area of a circle with radius 3
radius = 3
area = math.pi * (radius ** 2) # Using math.pi and the power operator
print(f"The area of a circle with radius {radius} is {area}") # Output: The area of a circle with radius 3 is 28.274333882308138

In this example:

• import math makes the math module available.
• math.sqrt() calls the sqrt function inside the math module.
• math.pi accesses the pi constant from the math module.

Importing Multiple Modules

If you need functions or variables from several different modules, you can import them separately. The standard practice is to put each import statement on its own line at the top of your file:

import math
import random # Another standard library module for random numbers
import os     # Module for interacting with the operating system

print(math.sqrt(100))
print(random.randint(1, 10)) # Get a random integer between 1 and 10
print(os.getcwd())           # Get the current working directory

This simple import module_name statement, combined with dot notation, is the most common and recommended way to bring external code into your Python scripts, ensuring clarity and preventing name collisions. In the next sections, we'll look at variations of the import statement and explore Python's standard library further.