7 Things I Wish I Knew Earlier About Python Classes

Liu Zuo Lin

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Level Up Coding

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4 days ago

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Day 90 of experimenting with video content:

1) __init__

class Dog:
  pass

dog = Dog()

^ this is a legal and valid Dog object. But it has no attributes, and we cannot do much useful stuff with this object.

class Dog:
  def __init__(self, name, age):
    self.name = name
    self.age = age

# create Dog object with name='rocky' & age=5
dog = Dog('rocky', 5)

^ using __init__, we can allow our users to assign attributes to our objects eg. name and age for our Dog class. Which makes our objects a lot more useful.

2) __str__

class Dog:
  def __init__(self, name, age):
    self.name = name
    self.age = age

dog = Dog('rocky', 5)

print(dog) # <__main__.Dog object at 0x1042dfd40>

^ by default, when we print our Dog object dog, we get this gibberish.

class Dog:
  def __init__(self, name, age):
    self.name = name
    self.age = age

  def __str__(self):
    return f'Dog(name={self.name} age={self.age})'

dog = Dog('rocky', 5)

print(dog)  # Dog(name=rocky age=5)

^ by defining our own __str__ method, we override the default behaviour above, and control our object’s behaviour when we do str(dog) (which is automatically done when we use print())

3) __dict__

class Dog:
  def __init__(self, name, age):
    self.name = name
    self.age = age

dog = Dog('rocky', 5)

^ a simple Dog class

dog = Dog('rocky', 5)

print(dog.__dict__) # {'name': 'rocky', 'age': 5}

^ the __dict__ attribute is a dictionary containing all attributes of our object. This is useful to inspect complicated objects and classes with many many attribtues.

4) super().__init__

Let’s define 2 classes — Rectangle and Square

• Rectangle has 4 sides and 4 right angles