Python Modules and Packages

Modules and Packages

The Python standard library includes may useful tools for a wide range of tasks.
This feature is sometimes called “batteries included”.
Python organizes libraries into modules that can be used in Python scripts.
There are also many third-party tools and packages that offer more specialized functionality.

The `import` Statement

The import statement loads built-in and third party modules and can be used in various ways:
- Explicit import (preserves the modules content in a namespace)
```
import math
math.cos(math.pi)
```
- Explicit import by alias
```
import math as m
m.cos(m.pi)
```
- Explicit import of module contents
```
from math import cos, pi
cos(pi)
```
- Implicit import of module contents
```
from math import *
cos(pi)
```

Python Module Conventions

A Python script can be treated as a module (imported into another Python program) or as a stand alone program.

A runnable script typically has a this statement

if __name__ == '__main__':
    # statements that should not
    # be executed when imported
    # into another file

The code in the main block will not be executed when the file is imported.

Useful Standard Library Modules

os and sys: tools for interfacing with the operating system.
math: mathematical functions and operations
itertools: tools for constructing and interacting with iterators and generators.
random: tools for generating pseudorandom numbers
json and csv: tools for reading file formats.

Third-Party Modules

Python has modules that are not included in the standard library.
These modules can be imported like the standard library modules provided that they are installed.
Useful third-party modules:
- numpy: provides an efficient way to store and manipulate multi-dimensional dense arrays.
- pandas: provides a labeled interface to multi-dimensional data.
- matplotlib: provides a way to create scientific visualizations.