Import Mechanics¶

Python programs are typically organized into modules.

A module is simply a Python file containing functions, classes, and variables that can be reused by other programs.

The import statement allows one module to access definitions from another.

flowchart LR
    A[Module A] -->|import| B[Module B]
    B --> C[functions]
    B --> D[classes]
    B --> E[variables]
````

---

## 1. What Is a Module?

A module is a file ending in `.py`.

Example file:

```python
# math_utils.py

def square(x):
    return x * x

Another program can use this function by importing the module.

import math_utils

print(math_utils.square(5))

2. Basic Import Syntax¶

The simplest form:

import module_name

Example:

import math

print(math.sqrt(9))

Output:

3.0

The module name acts as a namespace.

3. Importing Specific Names¶

Sometimes only certain functions are needed.

from math import sqrt

print(sqrt(16))

This allows calling sqrt() directly without the module prefix.

4. Import Aliases¶

Modules can be imported with shorter names.

import numpy as np

Example:

import math as m

print(m.sqrt(25))

Aliases make code shorter and more readable.

5. Importing Multiple Names¶

from math import sqrt, sin, cos

6. How Python Finds Modules¶

Python searches for modules in several locations.

flowchart TD
    A[import statement]
    A --> B[current directory]
    B --> C[installed packages]
    C --> D[standard library]

This search path is stored in sys.path.

7. The Standard Library¶

Python includes many built-in modules.

Examples:

Example:

import random

print(random.randint(1, 10))

8. Worked Example¶

Create a module:

# geometry.py

def area_square(x):
    return x * x

Use it:

import geometry

print(geometry.area_square(4))

Output:

16

9. Summary¶

Key ideas:

• modules are Python files containing reusable code
• import loads a module
• from module import name imports specific objects
• aliases can simplify code
• Python searches several locations when importing modules

Modules help organize programs and promote code reuse.