When implementing your classes for a project, you will likely want specific ways you can quickly create objects from that class. So far, we’ve created objects with some default, blank data. There is a nice way to set up an object that gives us control of the process. These are called constructors, sometimes referred to as initializers. A constuctor is a special method defined in a class definition that is responsible for setting up, or constructing an object. You’ve used constructor methods in previous demos, specifically when you created an object. In the previous program, the Dog() method constructed a dog object. It wasn’t explicitly defined in the class definition, but a default one exists for any class that is defined. To implement your own constructor, create a method named __init__(), where init is short for initializer. Look at the example below:
class Car:
def __init__(self, make, model, year):
self.make = make
self.model = model
self.year = year
def drive(self):
print("Driving to destination.")
The above Car class has a constructor defined that requires a make, model, and year arguments to be passed in. This method can be set up like any other function, such as specifying default argument values, variable length arguments, etc.
class Cat:
def __init__(self, name, breed="domestic shorthair"):
self.name = name
self.breed = breed
def meow(self):
print(f"{self.name}: Meow...")
In the Cat class, only a name is required. The constructor will set the cat’s breed to domestic shorthair if a breed argument is not specified. Notice in both examples that I can directly specify the instance variables right in the constructor. I don’t need to redundantly initialize any variables up above. That’s where the self keyword comes in play.
You may remember self from the Dog class. self is a special keyword that references the current object in use. To clarify this, let’s make some cat objects using the class above.
cat1 = Cat("Lilly", "Siamese")
cat2 = Cat("Late")
cat1.meow()
If I call the meow method, how does Python know the value of self.name? Whenever a method is called, the current object in use will be referenced with self. So, since cat1, Lilly, is the given object, self is the cat Lilly. On a side note, you can call this parameter whatever you want, but the convention is call it ‘self’.
Warning: You will be creating a second Python file for the first time. Read the instructions below carefully!
pokemon.py
from random import randint
from math import floor
class Pokemon:
# Required arguments: name, type
# Optional arguments: hp, lvl, xp
def __init__(self, name, type, hp = 20, lvl = 1, xp = 0):
self.name = name
self.type = type
self.hp = hp
self.lvl = lvl
self.xp = xp
# Damage = current level * 1.5 + random number; round down
def attack(self):
return floor(self.lvl * 1.5 + randint(2, 5))
def rest(self):
self.hp += randint(2, 4)
main.py
from random import randint
from pokemon import Pokemon
pokemon1 = Pokemon("Squirtle", "water")
pokemon2 = Pokemon("Gengar", "ghost", 23, xp=50)
enemy_pokemon1 = Pokemon("Abra", "psychic", 12)
enemy_pokemon2 = Pokemon("Bulbasaur", "grass")
won_battle = False # Switch to True if battle is won
choice = ""
# Player chooses Pokemon
while choice != "1" and choice != "2":
print(choice)
print("Choose your Pokemon!")
print(f"1) {pokemon1.name}")
print(f"2) {pokemon2.name}\n")
choice = input("(1 or 2) -> ")
if choice == "1":
player_pokemon = pokemon1
elif choice == "2":
player_pokemon = pokemon2
else:
print("Invalid, try again.")
print(f"\nYou chose {player_pokemon.name}!")
# Enemy chooses Pokemon
random_choice = randint(1, 2)
if random_choice == 1:
enemy_pokemon = enemy_pokemon1
else:
enemy_pokemon = enemy_pokemon2
print(f"Sleepy Mortimer chooses {enemy_pokemon.name}!\n")
# Begin Match
print(f"----- Match: {player_pokemon.name} vs. {enemy_pokemon.name}! -----\n")
while player_pokemon.hp > 0 and enemy_pokemon.hp > 0:
print("*************")
print(f"{player_pokemon.name}: {player_pokemon.hp}hp")
print(f"{enemy_pokemon.name}: {enemy_pokemon.hp}hp\n")
print("1) Attack")
print("2) Rest")
print("*************")
choice = input("-> ").lower()
# Player Turn
if choice == "1" or choice == "attack":
damage = player_pokemon.attack()
print(f"{player_pokemon.name} does {damage} damage!")
enemy_pokemon.hp -= damage
if enemy_pokemon.hp <= 0:
print(f"{enemy_pokemon.name} fainted!")
won_battle = True
elif choice == "2" or choice == "rest":
player_pokemon.rest()
print(f"{player_pokemon.name} rested and now has {player_pokemon.hp}hp.")
else:
print(
f"You gave {player_pokemon.name} an incorrect command. They hesitate and lose a turn!")
# Enemy Turn - They can only attack if they haven't fainted
if enemy_pokemon.hp > 0:
random_choice = randint(1, 4) # 75% chance attack, 25% chance rest
if random_choice <= 3:
damage = enemy_pokemon.attack()
print(f"{enemy_pokemon.name} does {damage} damage!")
player_pokemon.hp -= damage
if player_pokemon.hp <= 0:
print(f"{player_pokemon.name} fainted!")
else:
enemy_pokemon.rest()
print(f"{enemy_pokemon.name} rested and now has {enemy_pokemon.hp}hp.")
# See who won the battle
if won_battle:
gained_xp = randint(5, 10)
player_pokemon.xp += gained_xp
print(f"You win! {player_pokemon.name} gained {gained_xp}xp!")
else:
print("You lose!")
Choose your Pokemon!
1) Squirtle
2) Gengar
(1 or 2) -> 2
You chose Gengar!
Sleepy Mortimer chooses Bulbasaur!
----- Match: Gengar vs. Bulbasaur! -----
*************
Gengar: 23hp
Bulbasaur: 20hp
1) Attack
2) Rest
*************
-> 1
Gengar does 4 damage!
Bulbasaur does 5 damage!
*************
Gengar: 18hp
Bulbasaur: 16hp
1) Attack
2) Rest
*************
-> 1
Gengar does 4 damage!
Bulbasaur does 5 damage!
*************
Gengar: 13hp
Bulbasaur: 12hp
1) Attack
2) Rest
*************
-> 2
Gengar rested and now has 15hp.
Bulbasaur does 3 damage!
*************
Gengar: 12hp
Bulbasaur: 12hp
1) Attack
2) Rest
*************
-> 1
Gengar does 4 damage!
Bulbasaur rested and now has 12hp.
*************
Gengar: 12hp
Bulbasaur: 12hp
1) Attack
2) Rest
*************
-> 1
Gengar does 6 damage!
Bulbasaur does 5 damage!
*************
Gengar: 7hp
Bulbasaur: 6hp
1) Attack
2) Rest
*************
-> 1
Gengar does 5 damage!
Bulbasaur rested and now has 4hp.
*************
Gengar: 7hp
Bulbasaur: 4hp
1) Attack
2) Rest
*************
-> 1
Gengar does 5 damage!
Bulbasaur fainted!
You win! Squirtle gained 10xp!