A method is a function contained in a class. It describes behavior for objects created from that class and commonly receives the instance as an additional Python argument named self. Through self, a method can read or change the object’s attributes, or state. section 2.2.2 section 3.2.1
Methods become useful when several functions repeatedly share data or pass results between one another. Grouping those related behaviors with their data in a class gives the object a focused set of responsibilities instead of leaving loosely connected functions scattered through the program. section 2.2.2 section 3.2.1
Turning game functions into methods
A Rock, Paper, Scissors simulator can move functions such as get_computer_choice(), print_options(), and print_choices() inside a RockPaperScissorsSimulator class. Each method then uses self where it needs the simulator instance. An __init__ method can establish self.computer_choice and self.human_choice before simulate() coordinates the steps. The object is used as RPS = RockPaperScissorsSimulator(); RPS.simulate(). section 2.2.2
Listing 2.4. Moving functions into a class as methods
import random
OPTIONS = ['rock', 'paper', 'scissors']
class RockPaperScissorsSimulator:
def get_computer_choice(self): #1
return random.choice(OPTIONS)
def get_human_choice(self):
choice_number = int(input('Enter the number of your choice: '))
return OPTIONS[choice_number - 1]
def print_options(self):
print('\n'.join(f'({i}) {option.title()}' for i,
option in enumerate(OPTIONS)))
def print_choices(self, human_choice, computer_choice): #2
print(f'You chose {human_choice}')
print(f'The computer chose {computer_choice}')
def print_win_lose(self, human_choice, computer_choice,
human_beats, human_loses_to):
if computer_choice == human_loses_to:
print(f'Sorry, {computer_choice} beats {human_choice}')
elif computer_choice == human_beats:
print(f'Yes, {human_choice} beats {computer_choice}!')
def print_result(self, human_choice, computer_choice):
if human_choice == computer_choice:
print('Draw!')
if human_choice == 'rock':
self.print_win_lose('rock', computer_choice, 'scissors', 'paper')
elif human_choice == 'paper':
self.print_win_lose('paper', computer_choice, 'rock', 'scissors')
elif human_choice == 'scissors':
self.print_win_lose('scissors', computer_choice, 'paper', 'rock')
Inspect the short refactoring example to see ordinary functions become class methods and receive self. section 2.2.2
A method can also help control an interface. In a Greeter class, _day() and _part_of_day() can remain internal helpers while greet() exposes the main operation. This keeps callers focused on greeting rather than on the details used to construct the message. section 3.3
