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Modules

Modules are files containing Python code. They can define functions, classes, and variables. Python modules are imported using the import keyword.

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# Import the math module
import math

# Use the math module
print(math.sqrt(16))

# Output:
# 4.0

Importing Specific Items

You can import specific items from a module using the from keyword.

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# Import the sqrt function from the math module
from math import sqrt

# Use the sqrt function
print(sqrt(16))

# Output:
# 4.0

Aliasing Modules

You can alias a module using the as keyword.

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# Import pandas module and alias it as pd
import pandas as pd # this is a common data science convention

# Use the pd alias
df = pd.DataFrame()

# Output:
# Empty DataFrame
# Columns: []
# Index: []

Standard Library

Python comes with a standard library that provides a wide range of modules for performing various tasks. You can find the list of standard library modules here.

Third-Party Libraries

In addition to the standard library, Python has a vast ecosystem of third-party libraries that can be installed using package managers like pip. Some popular third-party libraries include:

  • NumPy: For numerical computing.
  • pandas: For data manipulation and analysis.
  • Matplotlib: For data visualization.
  • TensorFlow: For machine learning.
  • Django: For web development.

You can find a list of Python packages here.

Creating Your Own Modules

Modules help break down large programs into smaller, more manageable pieces. You can create your own modules by defining functions, classes, and variables in a Python file.

For example, let's say you have the following directory structure:

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myproject/
    main.py
    mymodule.py
mymodule.py
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# Create a module named mymodule.py
# mymodule.py
def greet(name):
    print(f"Hello, {name}!")
main.py
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# Import the greet function from mymodule
from mymodule import greet

# Use the greet function
greet("Alice")

# Output:
# Hello, Alice!

When you import your own modules from another file, Python searches the same directory, plus entries on sys.path / PYTHONPATH and any installed packages. The simplest case — both files in the same directory — works without extra configuration.

Setting Up a Directory as a Package

Since Python 3.3 (PEP 420), a directory can be a namespace package without __init__.py, but including an (even empty) __init__.py is still the clearest convention and required by some tools. For example, let's say you have a directory named mypackage with the following structure:

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myproject/
    main.py
    mypackage/
        __init__.py
        module1.py
        module2.py

To import the mypackage directory as a package, you can leave __init__.py empty (or add package initialisation code), then import submodules explicitly:

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from mypackage import module1, module2

# Use the module1 and module2 modules
module1.foo()
module2.bar()

Summary

Modules allow you to import different pieces of code and structure large projects.