What\'s the Key Difference Between Python Modules and Packages?

Understanding the Difference Between Modules and Packages in Python

Unlike many other programming languages, Python distinguishes between modules and packages. A clear understanding of their distinctions is crucial for effective Python coding.

Definition of a Module

A module in Python is nothing more than a single Python file. It is essentially a collection of code defined in that particular file. For instance, a file named "my_module.py" would define a module known as "my_module." Modules help organize code into logical units and enable importing and reusing them in other Python scripts.

Definition of a Package

A package, on the other hand, represents a collection of modules and sub-packages. It is represented by a directory containing multiple Python modules. Additionally, a file named "__init__.py" is required within the package directory to distinguish it from ordinary directories housing Python scripts. Packages may be nested at different levels, as long as each directory includes its own "__init__.py" file.

Distinctions Between Modules and Packages

While a module exists as a single Python file, a package constitutes a directory of Python modules. This distinction, however, only applies at the file system level. When importing either a module or a package, the generated Python object is always of type "module."

One notable difference is that importing a package only makes the variables, functions, and classes defined in its "__init__.py" file directly available. Sub-packages and modules within the package remain inaccessible through direct import.

Example

Consider the Python standard library's xml package as an illustration. Its xml directory holds an "__init__.py" file and four sub-directories. One of these sub-directories, etree, further contains an "__init__.py" file and a file called ElementTree.py.

Importing the various components would result in the following outcomes:

import xml
type(xml)  # <type 'module'>
xml.etree.ElementTree  # AttributeError: 'module' object has no attribute 'etree'

import xml.etree
type(xml.etree)  # <type 'module'>
xml.etree.ElementTree  # AttributeError: 'module' object has no attribute 'ElementTree'

import xml.etree.ElementTree
type(xml.etree.ElementTree)  # <type 'module'>
xml.etree.ElementTree.parse  # <function parse at 0x00B135B0>

From these examples, you can see that only after explicitly importing the sub-package or module (xml.etree.ElementTree) can you access its contents.

Note: Python also offers built-in modules that are implemented in C (e.g., sys). However, these fall outside the scope of your inquiry.

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