A Singleton pattern in python is a design pattern that allows you to create just one instance of a class, throughout the lifetime of a program. Using a singleton pattern has many benefits. A few of them are: To limit concurrent access to a shared resource.
I was missing the explanation, on why you would do this? What are the applications? And why always use person as an example, which doesn't say anything. Couldn't you have used a more applied example? Other than that, I love your videos! Please keep up the good work!
Consider a large code base, in which there are multiple modules that share config files. Instead of reading the files multiple times (too many I/O) across these modules we read it only once. Singleton is abstraction or illusion to share objects and states globally.
Think about designing a game of chess where you would wan't to save the state of the game in a class.. now you would want only one instance of the class in the whole software.... That's where we can use singleton
Python programmers almost never implement the Singleton Pattern as described in the Gang of Four book, whose Singleton class forbids normal instantiation and instead offers a class method that returns the singleton instance. Python is more elegant, and lets a class continue to support the normal syntax for instantiation while defining a custom __new__() method that returns the singleton instance. But an even more Pythonic approach, if your design forces you to offer global access to a singleton object, is to use The Global Object Pattern instead.
implementation using meta-class class MetaSingleton(type): _instances = {} def __call__(cls, *args, **kwargs): if cls not in cls._instances: cls._instances[cls] = super(MetaSingleton, cls).__call__(*args, **kwargs) return cls._instances[cls] class MyClass(metaclass=MetaSingleton): ...
A Singleton pattern in python is a design pattern that allows you to create just one instance of a class, throughout the lifetime of a program. Using a singleton pattern has many benefits. A few of them are: To limit concurrent access to a shared resource.
Imagine a game with a player class. There should only ever be one instance of player, and it needs to be accessed from many other classes. Using a singleton for player makes it easy to get a reference to this player instance from any class which needs to.
Nicely explained. But if you call get_instance() before PersonSingleton(), then it will return None, you forgot to do cls.__instance == PersonSingleton(*args)
This solution, to some extent confuses singleton with static, unfortunately. A singleton object does not use static data and uses a factory for creation.
This is an overly-complex solution. Don't need any abstractions or classes. All you need is a global variable + 1 function. Feels like you're writing Java in Python my dude.
from abc import ABCMeta, abstractstaticmethod class IPerson(metaclass=ABCMeta): @abstractstaticmethod def get_data(): """Implement in child class""" class SingletonPattern(IPerson): __instance = None def __new__(cls, *args, **kwargs) -> None: # new is already a static dunder method. if not cls.__instance: cls.__instance = super().__new__(cls) return cls.__instance
def __init__(self, username): # if not hasattr(self, "username"): prevents many instances self.username = username # else: # raise Exception("This class is a singleton") notifies error @staticmethod def get_data(): print(f"Username: {SingletonPattern.__instance.username}") if __name__ == "__main__": person = SingletonPattern("Kevin").get_data() person = SingletonPattern("John").get_data()
A Singleton pattern in python is a design pattern that allows you to create just one instance of a class, throughout the lifetime of a program. Using a singleton pattern has many benefits. A few of them are: To limit concurrent access to a shared resource.
I wanted to ask for more elaboration on the benefit you provided and perhaps other benefits this pattern brings?
I was missing the explanation, on why you would do this? What are the applications? And why always use person as an example, which doesn't say anything. Couldn't you have used a more applied example? Other than that, I love your videos! Please keep up the good work!
Consider a large code base, in which there are multiple modules that share config files. Instead of reading the files multiple times (too many I/O) across these modules we read it only once.
Singleton is abstraction or illusion to share objects and states globally.
Think about designing a game of chess where you would wan't to save the state of the game in a class.. now you would want only one instance of the class in the whole software....
That's where we can use singleton
same here, he never explains why???
It’s like taking a unique snapshot of the state?
I swear I learn more from you than from college
fu** college ,
i got nothing from that hell hole.
Why do you need to create an interface for this singleton example??🤔🤔
Python programmers almost never implement the Singleton Pattern as described in the Gang of Four book, whose Singleton class forbids normal instantiation and instead offers a class method that returns the singleton instance. Python is more elegant, and lets a class continue to support the normal syntax for instantiation while defining a custom __new__() method that returns the singleton instance. But an even more Pythonic approach, if your design forces you to offer global access to a singleton object, is to use The Global Object Pattern instead.
Can we make this pattern look more "pythonic" by overriding the __new__ static method instead of introducing get_instance?
more like the metaclass would override the __call__ function instead
great video, i'm actually learning a from the *design pattern* videos
thank you floren. need more video on the rest of the common design pattern.
These series is excellent, thanks!
And what would be the point of this?
implementation using decorator
def singleton(cls):
instances = {}
def getinstance():
if cls not in instances:
instances[cls] = cls()
return instances[cls]
return getinstance
@singleton
class MyClass:
...
implementation using meta-class
class MetaSingleton(type):
_instances = {}
def __call__(cls, *args, **kwargs):
if cls not in cls._instances:
cls._instances[cls] = super(MetaSingleton, cls).__call__(*args, **kwargs)
return cls._instances[cls]
class MyClass(metaclass=MetaSingleton):
...
Just what I needed, thank you so much!
Hey! A very clear explanation as usual. A suggestion, you could display your video on the bottom left , that way it won't block any text.
3:09 Never use sth == None. pep8 does not recommend that. Instead, use sth is None.
imagine being a complete python noob and watching this..
Hahahaha I hope they would read "Advanced" before watching ^^
@@NeuralNine they should..
@@NeuralNine 🤣🤣🤣
Great explanation! I'm still trying to figure out where this pattern can be used. Anyway. Thanks!
A Singleton pattern in python is a design pattern that allows you to create just one instance of a class, throughout the lifetime of a program. Using a singleton pattern has many benefits. A few of them are: To limit concurrent access to a shared resource.
Imagine a game with a player class. There should only ever be one instance of player, and it needs to be accessed from many other classes. Using a singleton for player makes it easy to get a reference to this player instance from any class which needs to.
Why do we need, or do we need the IPerson class at all?
Why creating get_instance method if you don't use it ?
Really you are the best bro!!!!!!!!!!👍👍👍
I think you should add thread lock. So it will make it thread safe
Can we inherit from this singleton class?
Shouldnt this work without using Metaclass?
yes it should, I think he implemented it the way he did so that'd it'd be similar to a Java singleton
Nicely explained. But if you call get_instance() before PersonSingleton(), then it will return None, you forgot to do cls.__instance == PersonSingleton(*args)
Great video but you should be using 'is' and 'is not' for comparison against None.
Hi bro . Help me I can't understand about this pattern topic can you explain pls? And how many types are there?
This solution, to some extent confuses singleton with static, unfortunately. A singleton object does not use static data and uses a factory for creation.
This guy looks like Henry Cavill! Keep up the good work.
Great explanation. Thanks
Thanks for sharing!
nice one
Great tutorial
Don't treat Python as Java. There are better ways to deal with the Singleton functionality.
Like as ??😊
Nice bro 👍👍
Can you do a video course to make a discord bot?
I also said him in the last vid for discord.py
Yea!!
why does he look like a 3d rendered model?
awesome !!!
It’s great
This is an overly-complex solution. Don't need any abstractions or classes. All you need is a global variable + 1 function.
Feels like you're writing Java in Python my dude.
This is actually the correct way and how you should do it in production.
Fun fact: fun fact is fun
خوستيقة اسكت
Lol
@@mohamedkaci3485 ههههههههه
please, continue)
there is a pythonic way for singleton
I Want BETTER GUI CHAT :):):)
Cool tutorial! However, the get_instance and print_data should be class methods!
For the pattern, you actually only need the class member __instance and the logic in the __init__ function with the get_instance function.
print_data kind of exists as the __str__
method
make metaclass tutorial please
u look like gta charector
If you are noob in python ! Don't watch this
Nice video! What about RJVX12 algorithm review?
from abc import ABCMeta, abstractstaticmethod
class IPerson(metaclass=ABCMeta):
@abstractstaticmethod
def get_data():
"""Implement in child class"""
class SingletonPattern(IPerson):
__instance = None
def __new__(cls, *args, **kwargs) -> None: # new is already a static dunder method.
if not cls.__instance:
cls.__instance = super().__new__(cls)
return cls.__instance
def __init__(self, username):
# if not hasattr(self, "username"): prevents many instances
self.username = username
# else:
# raise Exception("This class is a singleton") notifies error
@staticmethod
def get_data():
print(f"Username: {SingletonPattern.__instance.username}")
if __name__ == "__main__":
person = SingletonPattern("Kevin").get_data()
person = SingletonPattern("John").get_data()