Object-Oriented Programming

  • Polymorphism: Multiple objects with the same method name, can use them the same way
    • Accomplished using duck-typing (no inheritance) or inheritance (use same base class)
    • Abstract Base Class (ABC): A base class that defines what methods the children must have, cannot be instantiated directly and uses @abstractmethod decorators
  • Classes can inherit from more than one parent class, conflicting method names are resolved using the Method Resolution Order (MRO)
  • @property turns a method into an attribute, can define a setter, getter, and deleter without having to add a new attribute

Design Patterns

  • Creational Patterns: Control how objects are created
    • Factory: Create objects by passing in an identifier of which object you want, abstracts away the logic to instantiate
    • Singleton: Ensures that a class has only one instance
      • Implemented using the __new__ operator which creates and returns an instance; return the class instance if it already exists
    • Builder: Constructs objects step by step, adding on attributes and methods as requested
  • Structural Patterns: Define relationships between components
    • Decorator: Add behavior to a class or function without modifying it
      • Add parameters to a decorator by creating a decorator factory which adds another function on top of the decorator
    • Adapter: Convert one interface into another
    • Composite: Treat individual objects and groups uniformly
  • Behavioral Patterns: Manage communication and control flow between objects
    • Strategy: Enapsualtes interchangeable algorithms
    • Observer: Notifies dependent objects (subscribers) of state changes
      • Objects subscribe to the observer, and the server notifies them of changes to the state
    • Command: Encapusales requests as objects
    • Iterator: Access elements one at a time
      • Implemented using __iter__ and __next__
    • Generator: Uses yield to produce values one at a time

Parallel Computing

  • A process has its own memory space, CPU context, execution flow, and resources; each Python process has its own, separate interpreter
    • Each process runs independently from each other and cannot interact with each other unless using shared memory or TCP
  • A thread is a part of a process, can run multiple threads that all execute concurrently
    • Use the same memory space as the process and are more lightweight, but have issues due to the Global Interpreter Lock (GIL) in Python, meaning that only one thread can truly run at a time
  • Threads are better for system responsiveness and handling multiple tasks at the same time that don’t need to be done concurrently, while processes are better for true parallelism
    • Threads are also good for when tasks spend time waiting, such as for network requests or database queries
  • Context switching: When the CPU switches from one task to another; requires multiple saves and loads of states
    • Threads context switch more often and faster but risk race conditions

Inter-Process Communication/Networking

  • IPC allows processes to exchange data and communicate
    • Leads to modular design, parallelism, and resource/time management
  • Types of IPC
    • Pipes: One-way stream between processes, used for parent-child communication
    • Named pipes: Like pipes but can be accessed by unrelated processes
    • Message queues: Send/receive messages using a queue, used for asynchronous messaging
    • Shared memory: Multiple processes use the same memory region, best for high-speed data sharing
      • Requires synchronization (due to race conditions and data overwriting) and is difficult to debug
    • Socket: Network-based communication through TCP/IP, best used for remote or cross-platform communication
    • Signals: Notifications between processes, used for interrupts, shutdowns, or alerts

Networking

  • Data exchange over wireless connections
  • Host: Device connected to a network
  • Protocol: Rules for communication
  • Packet: A chunk of data sent across the network
  • IP Address: Unique identifier for a device
  • Port: An endpoint for specific services
  • Open Systems Interconnection (OSI) model: Breaks networking into 7 layers, giving each layer a role in data transmission
    1. Physical
      • Transmits raw binary data over physical forms (eleectrical, optical, radio)
      • Defines hardware specifications for cables, connectors, etc.
      • Key characteristics include bandwidth, latency, attenuation, interference, propagation speed, cost, security, flexibility, distance limit
      • Includes ethernet cables and radio signals
    2. Data Link
      • Packages raw bits into frames for transmission and handles local delivery between devices
      • Manages MAC addressing, error detection, and access control ()
      • Includes ethernet and Wi-Fi
    3. Network
      • Handles logical addressing (IP address)
      • Determines best path for data to travel and enables internetworking (connecting networks together)
      • Breaks data into packets
      • Includes IP and routers
    4. Transport
      • Manages communication between devices and ensures complete, ordered, error-free delivery of data
      • Includes TCP (connection-oriented) and UDP (connectionless) services
        • TCP guarantees delivery, order, and error-checking and has flow control but is slower; used for web browsing, email, file transfer
        • UDP has no guarantees but is much faster; used for streaming, gaming, or VoIP (Voice over IP)
    5. Session
      • Handles logical sessions between applications
      • Coordinates dialogue control and supports checkpointing and recovering in long-running data exchanges
      • Includes RPC, VoIP setup and teardown
    6. Presentation
      • Converts data into an understandable format for applications, encrypting and decrypting data
      • Optimizes bandwidth usage using compression and ensures data interoperability
      • Includes JSON formatting, JPEG/MP3 encoding
    7. Application
      • Provides network services directly to applications, enabling data exchange, browsing, messaging, file transfer
      • Defines protocols for different tasks
      • Includes HTTP, FTP, DNS
  • A socket enables communication between processes through writing code at Layer 7; the OS and network handles layers 1-6
    • Can choose either TCP or UDP
  • Client-server architecture: A server listens for requests and sends data to its clients
    • Multi-client servers must use parallelism to handle clients, like threading or multiprocessing