Modular Programming

Dr Ian Cornelius

Hello

Learning Objectives
1. Understand the concept of modular programming and its purposes in Python
2. Demonstrate your knowledge of using modules

Modular Programming

Breaking down large programming tasks into smaller tasks or modules
Individual modules can build up to create a larger application
Advantages:
- simplicity
  - modules focus on a small portion of a given problem
- maintainability
  - logical boundaries are enforced between the different problem domains
  - minimises interdependency between code making it more maintainable
- re-usability
  - functions in a single module can be re-used through an interface

Overview of Modules in Python

Three methods of defining a module:
- writing a module in the Python language
- writing a module in C and loading it dynamically
- using a built-in module, contained in the Python interpreter
Each modules content is accessed the same way, using the import keyword
A module is the same a code library
- files containing classes and functions that can be imported

Creating a Python Module

Create an ordinary Python file (“.py”) with some code
- i.e. a file called calculator.py

class Calculator:
    def __init__(self):
        pass
    def cube(self, x):
        return x * x * x
    def square(self, x):
        return x * x

These files may be stored in a separate directory
- i.e. in my example they are stored in modules
Modules stored in a separate directory need an __init__.py file
- assists the Python interpreter in locating the submodules
  - i.e. calculator.py

from . import calculator

Using a Module

A module can be used by importing the filename
- i.e. calculator.py can be imported by using:

from modules.calculator import Calculator

Functions can then be accessed from the Calculator class

calc = Calculator()
calc.cube(3)
calc.square(3)

Module Aliases

Aliases can be provided to a module when it is imported using the as keyword
Useful for shortening a module name
- i.e. Calculator could become Calc

from modules.calculator import Calculator as Calc

myCalc = Calc()
myCalc.cube(3)
myCalc.square(3)

Executing Modules as a Script

Modules in Python can be executed as script in the command-line as such:

python3 filename.py < arguments >

To read arguments from the command-line, you need to use the sys module
- additionally, you need to read the input from the commandline using the argv method

if __name__ == "__main__":
    import sys
    from modules.calculator import Calculator
    print(f"Cube of {int(sys.argv[1])} = {Calculator().cube(int(sys.argv[1]))}")

$ python3 math.py 2
  Cube of 2 = 8

Built-in Python Modules

Python consists of several built-in modules
- i.e. platform, os and sys
Contains resources for specific functionalities
- i.e. operating system management, file handling, network and database connectivity
Additional Resource:
- List of Built-In Modules

import platform

systemDetails = platform.system()

systemDetails = Windows

Listing all Functions in a Module

To determine all the functions or variable names in a module, the dir() function can be used

import platform

moduleDetails = dir(platform)

moduleDetails = [’_Processor’, ’_WIN32_CLIENT_RELEASES’, ’_WIN32_SERVER_RELEASES’, ‘builtins’, ‘cached’, ‘copyright’, ‘doc’, ‘file’, ‘loader’, ‘name’, ‘package’, ‘spec’, ‘version’, ’_comparable_version’, ’_component_re’, ’_default_architecture’, ’_follow_symlinks’, ’_get_machine_win32’, ’_ironpython26_sys_version_parser’, ’_ironpython_sys_version_parser’, ’_java_getprop’, ’_libc_search’, ’_mac_ver_xml’, ’_node’, ’_norm_version’, ’_os_release_cache’, ’_os_release_candidates’, ’_os_release_line’, ’_os_release_unescape’, ’_parse_os_release’, ’_platform’, ’_platform_cache’, ’_pypy_sys_version_parser’, ’_sys_version’, ’_sys_version_cache’, ’_sys_version_parser’, ’_syscmd_file’, ’_syscmd_ver’, ’_uname_cache’, ’_unknown_as_blank’, ’_ver_output’, ’_ver_stages’, ‘architecture’, ‘collections’, ‘freedesktop_os_release’, ‘functools’, ‘itertools’, ‘java_ver’, ‘libc_ver’, ‘mac_ver’, ‘machine’, ‘node’, ‘os’, ‘platform’, ‘processor’, ‘python_branch’, ‘python_build’, ‘python_compiler’, ‘python_implementation’, ‘python_revision’, ‘python_version’, ‘python_version_tuple’, ‘re’, ‘release’, ‘subprocess’, ‘sys’, ‘system’, ‘system_alias’, ‘uname’, ‘uname_result’, ‘version’, ‘win32_edition’, ‘win32_is_iot’, ‘win32_ver’]

Note, the dir() function can be used on all modules
- you can also use help() to find out information about the module

Goodbye

Questions?
- Post them in the Community Page on Aula
Contact Details:
- Dr Ian Cornelius, ab6459@coventry.ac.uk