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Python Flashcards

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OOP

TODO: Add concepts from 331

  1. What is Object-Oriented Programming (OOP)?
    • It is a method of programming that attempts to model some process or thing in the world as a class or object. A very nice way of thinking about structuring code.
  2. What is a Class?
    • A blueprint for creating objects. It contains methods (functions) and attributes (similar to keys in a dictionary).
  3. What is an Object?
    • An instance of a class. Objects are constructed from a class blueprint and contain their class’s methods and properties.
  4. What is Encapsulation?
    • The grouping of public and private attributes/methods into a programmatic class, making abstraction possible.
    • Key aspects:
      • Data hiding: Protects an object’s data/internal state from outside, exposing only what’s necessary.
      • Public interfaces: Functions that allow interaction with external code.
    • The goal is to expose the bare minimum and keep it “encapsulated.”
  5. What is Abstraction?
    • Exposing only the relevant data in a class interface while hiding the private attributes and methods (the “inner workings”) from users.

Python specific stuff

  1. __init__ method
    • It is the constructor of a class that defines how an object should be set up when created
    • Takes parameters for initializing instance attributes.
    • The first parameter is always self, referring to the instance being created.
class User:
    def __init__(self, name, age):
        self.name = name
        self.age = age
 
user1 = User("Alice", 19)
print(user1.name)  # Output: Alice
  1. Instance Attributes and methods
    • Instance Attributes: Attributes specific to an instantiated object (e.g., self.name, self.age).
    • Instance Methods: Operate with a specific instance of the class, always taking self as the first parameter, allowing access to instance attributes.
class User:
    def __init__(self, first, last, age):
	    # instance attributes
        self.first = first
        self.last = last
        self.age = age
 
	# instance method
    def full_name(self):
        return f"{self.first} {self.last}"
 
user1 = User("Kirby", "Kim", 0)
print(user1.full_name())  # Output: Kirby Kim
  1. What are Class Attributes?
    • Attributes shared by all instances of a class and the class itself. They are used less frequently than instance attributes.
    • Common uses include:
      • Keeping track of how many instances have been created.
      • Default or shared data.
      • Constants.
    • Used with the class name
class User:
    active_users = 0  # Class attribute
 
    def __init__(self, first, last, age):
        self.first = first
        self.last = last
        self.age = age
        User.active_users += 1  # Increment when a new user is instantiated
 
user1 = User("Kirby", "Kim", 0)
print(User.active_users)  # Output: 1
  1. What are Class Methods?
    • Methods that operate on the class itself, not on instances. They are often used for operations related to the class as a whole.
    • Class methods use the @classmethod decorator.
class Pet:
    total_pets = 0
 
    def __init__(self, name, species):
        self.name = name
        self.species = species
        Pet.total_pets += 1  # Increment total pets
 
    @classmethod
    def total_pet_num(cls):
        return f"Total pets: {cls.total_pets}"
 
print(Pet.total_pet_num())  # Output: Total pets: 0
  1. What is the repr method?
    • A method that provides a nice string representation of an object. It is called when you use the print() function or str() on an object.

How does Python know how to interpret the +  operator differently in these cases?

5 + 5 = 10
"5" + "5" = "55"
  • The 1st argument has a special method that defines what to do with the + operator
    • Python checks the type of the left operand.
    • It looks for the add() method in that operand’s class.
    • If the left operand’s class does not define add(), it checks the right operand’s class, and if both classes have it, the method from the left operand’s class is used.

Iterables and generators

  • What is an iterable in Python?
    • An iterable is an object that can return an iterator. It has an __iter__() method or defines a __getitem__() method that can take indexes. Examples include lists, strings, tuples, and files.
  • What is an iterator in Python?
    • An iterator is an object with state that keeps track of where it is during iteration. It implements the __next__() method to return the next item and raises StopIteration when there are no more items.
  • What is the difference between an iterable and an iterator?
    • An iterable is an object that can return an iterator, whereas an iterator is the object that actually performs the iteration, using the __next__() method to get each item.
  • Can an object be both an iterable and an iterator?
    • Yes, an object can be both an iterable and an iterator if it implements both iter() and next() methods, as in the case of some custom iterator classes.

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