Python Modules

Python Modules at a Glance

A module is a .py file containing Python code. Importing modules lets a program reuse functions, variables, and other definitions without keeping every task in one large file.

1. Create and Import a Module

Create a module by saving Python code in a separate file. The example below keeps the reusable function in connect_to_device.py and calls it from main.py.

def connect_message(device_name):
    print("Connection to %s in progress." % device_name)

import connect_to_device

connect_to_device.connect_message("FW1")

Connection to FW1 in progress.

The import statement uses the filename without the .py extension. Keep both files in the same project directory for this first example. The module name becomes a namespace, so the function is called as connect_to_device.connect_message().

2. Import a Module with an Alias

The as keyword gives a module a shorter or more meaningful local name. Use a clear alias and keep it consistent throughout the file.

import connect_to_device as ctd

ctd.connect_message("FW1")

Connection to FW1 in progress.

The alias changes only how this file refers to the imported module. It does not rename connect_to_device.py.

3. Variables in a Module

A module can contain variables as well as functions. Access an imported variable through the module namespace to show exactly where the value came from.

disconnect_message = "Disconnect in progress."

import connect_to_device

print(connect_to_device.disconnect_message)

Disconnect in progress.

4. Import Specific Names from a Module

You do not have to import the entire module namespace. The from ... import ... form brings selected functions or variables directly into the current file.

def connect_message(device_name):
    print("Connection to %s in progress." % device_name)

def disconnect_message(device_name):
    print("We are going to disconnect: %s." % device_name)

from connect_to_device import disconnect_message

disconnect_message("R1")

We are going to disconnect: R1.

5. Built-In Modules

Python includes a large standard library, so many common jobs do not require an external package. Examples include math for calculations, json for JSON data, os and pathlib for file-system work, sys for interpreter information, datetime for dates and times, re for regular expressions, smtplib for SMTP, ipaddress for IP networks, and subprocess for running system commands.

import math

print(math.pi)

3.141592653589793

Python can also list discoverable modules with help("modules"), although the result can be very long and may include third-party packages installed in the environment. Official documentation is usually easier to search.

6. Explore a Module with dir()

The dir() function returns the names available on an object. It is a quick way to see a module's functions, variables, constants, and Python-managed attributes.

import connect_to_device

print(dir(connect_to_device))

['__builtins__', '__cached__', '__doc__', '__file__',
 '__loader__', '__name__', '__package__', '__spec__',
 'connect_message', 'disconnect_message']

import math

print(dir(math))

['__doc__', '__file__', '__loader__', '__name__',
 '__package__', '__spec__', 'acos', 'ceil', 'cos',
 'factorial', 'floor', 'pi', 'sin', 'sqrt', 'tan']

Use dir() for quick exploration, then consult the module documentation to understand parameters, return values, exceptions, and examples.

7. Reuse a Module with a Loop

A focused module becomes more useful when a program applies the same tested behavior to multiple devices.

def show_connection_messages(device_name):
    print(f"Attempt to connect to {device_name} in progress.")
    print("Connection in progress")
    print("Connection successful!")

from connect_to_device import show_connection_messages

routers = ["R1", "R2", "R3"]
switches = ["SW1", "SW2"]

for router in routers:
    show_connection_messages(router)

for switch in switches:
    show_connection_messages(switch)

8. Conclusion

Modules turn one large script into smaller files with clear responsibilities. They make functions and variables reusable, expose Python's standard library, and help network automation projects stay easier to test and maintain.

• A module is a file containing Python code.
• Use import module_name to keep names under a clear namespace.
• Use as to assign a sensible local alias.
• Use from module_name import item when a direct name improves readability.
• Use built-in modules before rebuilding common functionality.
• Use dir() for quick discovery and documentation for complete guidance.