NSU Software Engineering in Python

In this course, you’ll learn the Software Engineering and Software Design disciplines which offer several methodologies how to build applications with a predefined level of quality. You’ll know the design approaches, principles and best practices which are powered by Python but can also be translated into other languages. These principles and practices are universal and touch almost everything from the software creation process: requirements gathering, analysis, architecture design, layering, subsystems design, testing, supporting. You’ll also know about various design principles and patterns: how they help to build a testable, maintainable, reliable and robust software that satisfies the requirements. You’ll see the applicability of Python’s duck typing, OOP interfaces, functional approaches, and other elements of the language we use to express the behavior we need.

Lecture Plan

Recommended Literature

• “Clean Code” Robert Martin
• “Code Complete” Steve McConnell
• “Refactoring” Martin Fowler
• “Domain-Driven Design: Tackling Complexity in the Heart of Software” Eric Evans
• “Clean Architecture” Robert Martin
• “Domain Specific Languages“ Martin Fowler
• “Design Patterns: Elements of Reusable Object-Oriented Software” (aka “Gang of Four’s Book”) Erich Gamma, Richard Helm, Ralph Johnson, & John Vlissides
• “Functional Design and Architecture” Alexander Granin

Part I. Software Design Basics

1. Introduction to Software Design

• Why, When, How
• The Big Picture
  • Software Lifecycle
    • Requirements Gathering & Analysis
    • Design of the Architecture
    • Design of the subsystems and components
    • Implementation, Testing
    • Deployment to Production
    • Support
  • Requirements Gathering
    • Q&A
    • Use Case diagrams (UML)
    • User Scenarios
    • Mind Maps
    • Whatever you want
  • Software Modeling
    • The Past: UML
    • The Present: whatever you want
  • Design Principles
  • Design Patterns
  • Design Approaches
  • Best Practices
  • Languages & Paradigms
  • Methodologies
• A single trick to rule them all
  • Interface (abstraction)
  • Implementation

2. Inversion of Control

• Interfaces design
  • Consistency
  • Completeness
  • Non-redundancy
  • Simplicity
  • Easy usage
  • Single Responsibility
• Dependency Inversion
• Inversion of Control

3. Layering & Modularity

4. Object-oriented idioms in Python

• Variables
• Tuples
• Immutability
• Shallow copy
• Deep copy
• Function parameters
• Garbage collection

5. ABC Interfaces

6. Design Principles: SOLID

7. Design Patterns 1

• OOP Design Patterns
• • Adapter
• • Visitor

8. Design Patterns 2

• • Singleton
• • Strategy
• • Decorator

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Math Assistant

Functional Requirements

• Knowledge Base with math objects which have name and description.
• Command-line application
• CLI Commands:
  • Finish: finish the CLI application finish
  • Describe: describe a notion from the Knowledge Base describe <name:str> describe "Number"`
  • Add: add a notion into the Knowledge Base add <name:str> <descr:str> add "some name" "some description"

Labyrinth

• Implement the "Labyrinth" game (aka "Terra Incognita").
  • Labyrinth (Wiki)
  • Terra Incognita
• You should use the knowledge obtained during the course.
• Design the game using:
  • Interfaces (OOP-like)
  • Inversion of Control
  • Dependency Injection
  • Proper layering
  • Proper project structure
  • Diagrams of classes and interaction between classes
• The code should be extensible enough to support new upcoming requirements (see "Mandatory set of rules" and "Extended set of rules").

Functional requirements

• "Labyrinth" is a one-player turn-by-turn game which should be implemented as a console application.
  • Game consists of labyrinth, labyrinth objects, user inventory, CLI interface.
  • Computer is a master of game.
  • Game is controlled by text commands.
  • Initially, the player can't see the labyrinth. The player should explore the labyrinth on its own.
• User commands:
  • Starting a new game with a predefined labyrinth size: "start <labyrinth_size>". Labyrinth size should be not less 4 and not bigger 10.
  • Quiting the current game: "quit" (without saving).
  • Quiting the current game with saving: "save <file_name>" (the game should be saved into a text file).
• On the start, labyrinth should be randomly generated.
  • Labyrinth consists of cells.
  • A wall can be built between any two neighbour cells.
  • An outside wall is called monolith.
  • There should be no inaccessible cells.
  • There should be one exit randomly dislocated in the monolith wall.

Mandatory set of rules

• Game flow:
  • Player's goal to find a treasure and leave the labyrinth.
  • Games starts after the labyrinth is generated.
  • On the start, player is invited to enter commands.
  • Game prints the results of processing the commands.
  • Game ends when the player leaves the labyrinth with a treasure.
  • If the player doesn't have a treasure found, the game should say he can't leave the labyrinth on attempt to pass through the exit.
• Game objects:
  • Treasure.
  • 5 wormholes, organized into a cyclic ordered set. Entering a wormhole moves the player into the next wormhole by index. Skipping a move while staying on the wormhole moves the player to the next wormhole.
• User commands:
  • Moving: "go up", "go down", "go left", "go right".
  • Skipping a turn: "skip".
• Game messages:
  • "step impossible, wall"
  • "step executed, wormhole"
  • "step executed, treasure"
  • "step impossible, monolith"
  • "step executed" (on successful moving)

Extended set of rules

• Game objects:
  • River. Has source and end. Several cells arranged in a chain which cannot intersect itself. Entering a river moves the player 2 cells down a stream (maximum). Skipping a turn triggers this moving again. River and wormholes cannot share the same cell.
  • Bear. Bear is like a player but moves randomly and is NPC. River and wormholes affect bear as well. Once bear and player step on the same cell, player becomes damaged. When damaged, the player should be also moved 1 cell away from the bear towards any passable direction. (If this is not possible, player stays where he was) Damaging the player second time makes him dead.
  • Map. When the player has a map he can use the "map" command to see the whole labyrinth (including treasure, bear, river, wormholes). Using this command behaves like skipping a turn (all the effects should be applied.)

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Assignment 1: Interfaces, implementations, Inversion of Control

Task 1: Interfaces, implementations, Inversion of Control

1. What is the purpose of an interface in software engineering?

2. Provide an example of an interface in Python.

3. Choose any business domain and write an example of an interface class and implementation of two derived classes. The interface must contain at least one function (e.g. printDescription) to print the object description to the console.

• the interface should inherit from abc.ABC
• the method in the interface should be decorated with @abstractmethod decorator

4. Design IOutputStream interface that contains at least one function (e.g. print) that prints the given string. And make at least two classes that implement this interface:

• ConsoleStream
• FileStream (What arguments the constructor should have?)

5. Rework the implementation of the classes from the #3. These classes must receive an IOutputStream object in the constructor and use it in the printDescription method instead of printing its description to the console.

• Each interface should be defined in a separate module.
• Create a python module containing the main function. Demonstrate the dependency injection (Inject IOutputStream into the classes from #3) Demonstrate printing the object description(from #3) into different OutputStreams. Why does this example demonstrate an inversion of control?