[Python] Tips : Special Method

Special Method?

Special Method, which is also called Magic Method, is a kind of method that can be set in user-defined class objects. It is usually surrounded by two Under-bars at head and tail of the keyword like __init__, __str__, etc.

Why do we need this?

With Spcial Method, your script must be more pythonic and more efficient.

You can

• Use the instance of the class as built-in types, such as data-types, functions, etc.

How to use Special Method

Take a look at the below code. At the bottom, I commanded to print() the parameter with the identifiter japan. At this, the japan is the instance of the class which I defined. So, the code prints the infomation of the type about the japan.

class country:
  def __init__(self, name, population):
    self.name = name
    self.population = population

japan = country('Japan', '125m')

print(japan)

# <__main__.country object at 0x7f0d90322290>

As Known, this is the expected output. However, there will be something different with Special Method.

class country:
  def __init__(self, name, population):
    self.name = name
    self.population = population
    
  # Add Specical Method inside the class
  def __str__(self):
    return f'name : {self.name}, population : {self.population}'

japan = country('Japan', '125m')

print(japan)

# name : Japan, population : 125m

At the bottom, I also commanded to print() the parameter with the identifiter japan. And then, the code prints the string from return of instance method '__str__()' inside the class japan.

Therefore, you can get string from class, just as parameter.

class country:
  def __init__(self, name, population):
    self.name = name
    self.population = population

japan = country('Japan', '125m')

japan()

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-3-88c499f4f664> in <module>()
      6 japan = country('Japan', '125m')
      7 
----> 8 japan()

TypeError: 'country' object is not callable

class country:
  def __init__(self, name, population):
    self.name = name
    self.population = population
  
  def __call__(self):
    print(f'name : {self.name}, population : {self.population}')

japan = country('Japan', '125m')

japan()

name : Japan, population : 125m