I want to get instance of one of subclasses when trying get instance of a superclass (parent class) depending on arguments. For example, I have parent class(I'm using python3):
class Man:
def __init__(self, name, age):
self.name = name
self.age = age
def say_hello(self):
print("Hello! My name is {}.".format(self.name))
And subclass:
class YoungMan(Man):
def say_hello(self):
print("Hey, man! Wazap?")
If age of Man less 30, I want it become YoungMan:
John = Man('John', 25)
type(John) #<class '__main__.YoungMan'>
John.say_hello() #Hey, man! Wazap?
I tried solve it with Man.__new__():
class Man:
def __new__(cls, name, age):
if age < 30:
return YoungMan(name, age)
else:
return super(Man, cls).__new__()
...
But John.say_hello() returns Hello! My name is John. So Man methods override YoungMan methods. After I tried use metaclass for Man:
class ManFactory(type):
def __call__(self, name, age):
if age < 30:
return YoungMan(name, age)
class Man(metaclass=ManFactory):
...
But it lached on ManFactory.__call__().
I understand that I can use a funtion John = get_Man(name, age) which returns right class, but it isn't so handsome. My question is about how do it like this:
John = Man('John', 25)
type(John) #<class '__main__.YoungMan'>
John.say_hello() #Hey, man! Wazap?
Brad = Man('Brad', 54)
type(Brad) #<class '__main__.Man'>
Brad.say_hello() #Hello! My name is Brad.
Not sure if this is good practice but you could set self.__class__:
class Man:
def __init__(self, name, age):
if age < 30: self.__class__ = YoungMan
self.name = name
self.age = age
def say_hello(self):
print("Hello! My name is {}.".format(self.name))
class YoungMan(Man):
def say_hello(self):
print("Hey, man! Wazap?")
a = Man("Brad", 15)
print(type(a))
>>><class '__main__.YoungMan'>
a.say_hello()
>>>Hey, man! Wazap?
The main problem with this method is that the YoungMan would still be constructed by Man.__init__() so the classes would have to be compatible. Creating a function get_man() is still the best solution.
Related
class Human():
def __init__(self, name, age):
self.name = name
self.age = age
def hablar(self, message):
print(message)
class Alien(Human):
def __init__(self, planet):
self.planet = planet
def fly(self):
print("I'm flying!")
This code is an example to show what I want to do. Imagine that I want an alien to inheritance all the properties of a Human but I also want him to have a planet attribute to distinguish from which planet does it comes.
When I do it as I did it in the mentioned code, it didn't work. Is it possible to do it? How?
Thanks!
You might want to refer to this question about calling parent class constructor from a child class.
You need to use the dunder method __init__ of the parent class inside the __init__ of Alien as so:
class Human():
def __init__(self, name, age):
self.name = name
self.age = age
def hablar(self, message):
print(str(message))
class Alien(Human):
def __init__(self, name, age, planet):
super().__init__(name, age)
self.planet = planet
def fly(self):
print("I'm flying!")
You need to reference the constructor of the parent class.
class Alien(Human):
def __init__(self, name, age, planet):
super().__init__(name, age)
self.planet = planet
class Human():
def __init__(self, name, age):
self.name = name
self.age = age
class Alien(Human):
def __init__(self, planet, **kwargs):
self.planet = planet
super(Alien, self).__init__(**kwargs)
Z = Alien(planet='Venus',name='Z',age=21)
print(Z.__dict__)
output:
{'planet': 'Venus', 'name': 'Z', 'age': 21}
Lets assume that I have a class called Person, and a class that inherits this called Group. Person has an attribute called name and one called age. When I create a Group I want to pass n person objects and their new name is a combo of names, and their new age is their combined age.
also for the hell of it, going to keep track of how many people, and how many groups there are separately (just so inheriting makes any sense in this example.)
class Person:
count = 0
def __init__(self, name, age):
self.name = name
self.age = age
self.id = make_person() # count is also the person's id in this example
def __str__(self):
return f'Name: {self.name} Age: {self.age}'
#classmethod
def make_person(cls):
cls.count += 1
return cls.count
class Group(Person):
def __init__(self, *people):
#not sure how to do this, Below Does Not Work, something like
new_name = self.make_group(people)
new_age = self.new_age(people)
self.name = new_name
self.age = new_age
super().__init__(self.new_name, self.new_age)
def make_group(self, *people):
return (' & ').join([person.name for person in People])
def new_age(self, *people):
return sum([person.age for person in people])
then you would think i could write
anne = Person('Anne', 20)
bob = Person('Bob', 20)
carl = person('Carl', 25)
couple = Group(anne, bob)
threesome = Group(anne, bob, carl)
print(couple)
print(threesome)
but this doesnt work. For some reason the group class isnt getting the people object i pass, or i'm defining it wrong...any ideas?
What you have written is that a Group is a particular type of Person. This doesn't seem quite right to me. Regardless, here is a version that will run and give the desired output:
class Person:
count = 0
def __init__(self, name, age):
self.name = name
self.age = age
self.id = Person.make_person() # count is also the person's id in this example
def __str__(self):
return f'Name: {self.name} Age: {self.age}'
#classmethod
def make_person(cls):
cls.count += 1
return cls.count
class Group(Person):
def __init__(self, *people):
#not sure how to do this, Below Does Not Work, something like
new_name = self.make_group(*people)
new_age = self.new_age(*people)
self.name = new_name
self.age = new_age
super().__init__(self.name, self.age)
def make_group(self, *people):
return (' & ').join([person.name for person in people])
def new_age(self, *people):
return sum([person.age for person in people])
anne = Person('Anne', 20)
bob = Person('Bob', 20)
carl = Person('Carl', 25)
couple = Group(anne, bob)
threesome = Group(anne, bob, carl)
print(couple)
print(threesome)
Changes from your code:
some typos with capital letters
put a * before people when passing it
take care of variable scope
Hi i have a python file that contains the class pets and a file conatins the class people and a main file
the code is this:
the pets code:
class Pet:
def __init__(self, name, age, sound, type):
self.name = name
self.age = age
self. sound = sound
self. type = type
class Dog(Pet):
def __init__(self, name, age):
super().__init__(name, age, "How How", "Dog")
class Cat(Pet):
def __init__(self, name, age):
super().__init__(name, age, "Mewo", "Cat")
this is the peoples file:
import Pets
class Person:
def __init__(self, gender, name, age):
self.gender = gender
self.name = name
self.age = age
self.pets = []
def addPet(self, pet):
if isinstance(pet, Pets.Pet):
self.pets.append(pet)
else:
print("This is not a pet pls try again.")
def printPets():
print("He has:")
for pet in self.pets:
print("A: " + pet.type+ " Named: " + pet.name)
And this is the Main file:
from Person import Person
import Pets
def Main():
p1 = Person("Male", "Bob", 18)
p1.addPet(Pets.Cat("Mitzi", 2))
p1.addPet(Pets.Dog("Rexi", 5))
print(p1.printPets)
if __name__ == "__main__":
Main()
the output that i get is:
<bound method Person.printPets of <Person.Person object at 0x7f413e3604e0>>
what is this and how do i fix it ??
thanx.
What you need is print(p1.printPets())
You need to invoke the method.
Else what you are doing is printing the method and what Python gives you is the method type (bound), instance type to which it belongs and address of the instance.
You just need to include () inside print() like this:
print(s1.avg())
I've tried reading a few different tutorials, but I still can't figure it out. I have two simple classes. Animal and cat.
class Animal:
def __init__(self, name):
self.name = name
class Cat(Animal):
def __init___(self, age):
self.age = age
print('age is: {0}'.format(self.age))
def talk(self):
print('Meowwww!')
c = Cat('Molly')
c.talk()
Output is:
Meowwww!
The code runs, but I'm a little confused. I created an instance of the cat class with c = Cat('Molly'). So somehow by using "Molly" as an argument for the Cat() class instance, it feeds "Molly" to the original base class (Animal) instead of the Cat class instance I created? Why? So how do I feed the Cat class instance the age variable it requires?
I tried doing:
c = Cat('Molly', 10)
But it complains about too many arguments. And secondly, why doesn't the __init__ function of the Cat class get called? It should print "age is...". It just never does.
EDIT: Got it to work, thanks to Martijn Pieters! Here is the updated code (works with python3):
class Animal():
def __init__(self, name):
self.name = name
print('name is: {0}'.format(self.name))
class Cat(Animal):
def __init__(self, name, age):
super().__init__(name)
self.age = age
print('age is: {0}'.format(self.age))
def talk(self):
print('Meowwww!')
c = Cat('Molly', 5)
c.talk()
You misspelled __init__:
def __init___(self, age):
# 12 345
That's 3 double underscores at the end, not the required 2.
As such, Python won't call it as it is not the method it is looking for.
If you want to pass in both age and name, give the method another argument, then call the parent __init__ with just the name:
class Cat(Animal):
def __init__(self, name, age):
super().__init__(name)
self.age = age
I am working on an assignment for Python Programming 157 at my school.
I need to write a class called Pet that has the following data attributes:
__name (for the name of the pet)
__animal_type (Examples: "Cat", "Dog", and "Hamster" )
__age (for the pet's age)
__height (for the pet's height)
It needs to include
set_name
get_name
I have tried like 4 times and cannot seem to get it right... any clues on getting it started?
# The Pet Program.
class PetProgram:
# The __init__ method accepts an argument for the program
# and adds it to the __pets attribute.
def __init__(self, pet):
self.__pets = pet
# The name will add to the pet attribute.
def name(self, name):
self.__pets = name
def age(self, age):
self.__pets = age
def animal(self, animal):
self.__pets = animal
def height(self, height):
self.__pets = height
# The pets_return will show you the list.
def pets_return(self):
return self.__pets
# The Pet Program.
import petsprogram
def main():
# Enter the name.
petname = input('What is the name of the pet: ')
print 'This will be added to the record.'
savings.name(petname)
# Display the list.
print petsprogram
main()
Above is my latest try...no such luck...any help? Thanks in advance...
A class is not a program, a class should model a thing, like a pet. Therefore, to start off, you should name your class appropriately.
class Pet(object): # Pet derives from the object class, always do this
Now I think you want a constructor that takes the name of the pet, and perhaps the type of pet as well, so we'll define that.
def __init__(self, pet_name, pet_type):
self.pet_name = pet_name
self.pet_type = pet_type
You also need a get and set for the name:
def get_name(self):
return self.pet_name
def set_name(self, pet_name):
self.pet_name = pet_name
To use this class, you instantiate it into an instance of the class:
puppy = Pet('Rover', 'Dog')
puppy.get_name() # prints Rover
I hope that's enough to get you going. You should read up on OOP in Python as mentioned in the comments.
First, why are you using "private" __attributes? That doesn't seem warranted.
Second, you're assigning all your properties to the same instance variable:
self.__pets = pet
self.__pets = name
self.__pets = age
self.__pets = animal
self.__pets = height
You should be using something like
def __init__(self, pet, name, age, animal, height):
self.pet = pet
self.name = name
self.age = age
self.animal = animal
self.height = height
and you should definitely read the tutorial on classes before venturing any further.
I'm not sure where the __pets binding comes into play. Your initial description doesn't say anything about that. I would not have expected an object that represents a pet, as in, a singular pet, to have an attribute that was a list of pets. I would expect something like:
class PetProgram:
def __init__(self, name ='', age=0, type='Unknown', height=0):
self.__name = name
self.__age = age
self.__animal_type = type
self.__height = height
def get_name(self):
return self.__name
def set_name(self, name):
self.__name = name
I'm also not sure where the imports petprogram comes from... is that perchance what your supposed to call your module, and then the instructor has provided that as something you're supposed to run to test it?
(also, what's with all the __under_scores? is this something your teacher is encouraging?)
How does something like this look?
>>> class Pets:
def set_Name(self,name):
self.name=name
def get_Name(self):
return self.name
def set_Atype(self,atype):
self.atype=atype
def get_Atype(self):
return self.atype
def set_Age(self,age):
self.age=age
def get_Age(self):
return self.age
def set_Height(self,height):
self.height=height
def get_Height(self):
return self.height