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Modules

What is a Module?

A module in Python is a file containing Python definitions and statements. The file name is the module name with the suffix .py added. Modules in Python serve as a way to organize code logically by grouping related functions, classes, and variables.

Creating a Module

Creating a module is as simple as writing Python code and saving it with a .py extension. For example, a file named my_module.py contains:

# my_module.py
def greeting(name):
    return f"Hello, {name}"

Importing Modules

You can use any Python file as a module by executing an import statement in another Python script or interpreter session. If my_module.py is in the same directory as your script, you can import it directly.

import my_module
print(my_module.greeting("Alice"))

Import with Alias

You can import a module with an alias using the as keyword. This is often used for modules with longer names.

import my_module as mm
print(mm.greeting("Bob"))

Importing Specific Items

To import specific functions, classes, or variables from a module:

from my_module import greeting
print(greeting("Charlie"))

Importing All Names (not recommended)

You can import all names (functions, variables, classes) from a module using *. This is generally discouraged as it can lead to unclear code.

from my_module import *
print(greeting("Dave"))

The Module Search Path

When a module is imported, Python searches for the module in a list of directories given by the variable sys.path. The search order is:

  • The directory containing the input script (or the current directory).
  • PYTHONPATH environment variable (a list of directory names, with the same syntax as the shell variable PATH).
  • The installation-dependent default (like /usr/local/lib/python).

Compiled Python Files

To speed up loading modules, Python caches the compiled version of each module in the __pycache__ directory under the name module.version.pyc, where "version" encodes the format of the compiled file.

Reloading a Module

The reload() function in the importlib module can be used to reload a previously imported module. This is useful if you have made changes to the module's source code and want to test these changes without restarting the interpreter.

from importlib import reload
reload(my_module)