Abstract Base Classes are non-instantiable classes used to define the expected behaviour of subclasses.
Questions tagged [abc]
280 questions
2
votes
0 answers
Flask-Login current_user changing to the most recent User class query result
My implementation of Flask-Login is working well across my site, with the exception of contexts where I need to make additional queries on the User class. For example, when I try to generate a list of User instances representing other users with…
user8155759
- 29
- 5
2
votes
1 answer
Abstract method allowing for additional arguments
Is it possible to have an abstract class require some specific arguments for a method of a Python class, while still leaving the possibility for concrete classes to add more arguments?
from abc import ABC, abstractmethod
class FooBase(ABC):
…
Jivan
- 21,522
- 15
- 80
- 131
2
votes
2 answers
Use __init_subclass__ to patch abstract methods while preserving the abc check
I would like to wrap an abstractmethod for all subclasses of an abc. I tried doing that by implementing __init_subclass__ as below:
import abc
class Base(abc.ABC):
@abc.abstractmethod
def foo(self) -> str:
pass
def…
tepsijash
- 370
- 2
- 18
2
votes
1 answer
How to create an abstract attribute for an abstract class in Python?
I already found some similar question where they try to create abstract attributes and they all suggest using @property and @abc.abstractmethod to achieve that like here. There are many similar topics but I cant find a way to do it without using the…
KZiovas
- 3,491
- 3
- 26
- 47
2
votes
1 answer
Is it OK to define optional methods on abstract base class?
Is it a good practice to have non-abstract methods on abstract base classes? I mean, methods that can, but don't have to, be present on subclasses of particular ABC?
Technically it is possible, as seen in the below example (ConcreteDataProvider does…
barciewicz
- 3,511
- 6
- 32
- 72
2
votes
1 answer
`__subclasshook__` on inherited abstract classes in Python?
I'm wondering how best I can define __subclasshook__ on a hierarchy of abstract classes in Python. Let's say I have an interface, and an ABC that inherits from that interface. Is something like this okay?
import abc
from typing import IO
class…
piglet
- 83
- 1
- 6
2
votes
1 answer
How to implement MutableSequence on custom class
I want to use a class like a list. I found out that inheriting and implementing collections.abc.MutableSequence makes the class list-like, but I don't know how to overload methods such as __getitem__, __setitem__ for integer and slice…
usan
- 81
- 1
- 8
2
votes
1 answer
In python, Can an abstract class be instantiated?
from abc import ABC, abstractmethod
class Example(ABC):
def smile(self):
print("smile")
My understanding is that Example becomes an AbstractClass when it inherits the ABC class. An AbstractClass can't be instantiated but
the following…
Kun.tito
- 165
- 1
- 7
2
votes
1 answer
How to implement a constructor for an abstract base class?
I am trying to write a base abstract class that has some properties that will be initialized using a constructor. So far I have this:
from abc import ABC, abstractmethod
class A(ABC):
def __init__(self, n, *params):
self.n = n
…
Farhood ET
- 1,432
- 15
- 32
2
votes
3 answers
ImportError: cannot import name 'my_function' from 'abc'
I'm trying to load python script from computer to google colab but is show me importError
Sandeep Agrawal
- 175
- 1
- 8
2
votes
0 answers
How do I tell pytype that an instance is a subclass of an abstract base, but not the abstract base itself?
The issue arises when code instantiates an instance of the supertype. Here's an example.
T = TypeVar("T")
class A(Generic[T], metaclass=abc.ABCMeta):
@abc.abstractmethod
def hello(self, arg: T):
raise NotImplementedError
class…
Carson McNeil
- 790
- 9
- 22
2
votes
1 answer
Is there some mechanism to enforce nested interfaces are implemented in abstract classes in Python?
I want to create a class that has some nested class that defines some contract in Python. A tenable example is a typed config object. My attempt at this is below:
from typing import Mapping
from abc import ABCMeta, abstractmethod
class…
erip
- 16,374
- 11
- 66
- 121
2
votes
0 answers
Python abstract base classes and multiple inheritance
I am trying to create a python (3.5) class structure where I use abstract methods to indicate which methods should be implemented. The following works as expected:
from abc import ABC, abstractmethod
class Base(ABC):
@abstractmethod
def…
Aaron
- 321
- 4
- 9
2
votes
0 answers
Register subclass to an ABC class inside __init_subclass__ does not fully work
What I want to achieve is to register one type as subtype of all other types. For some other reason I cannot use metaclass, so __init_subclass__ seems like a reasonable choice.
I have code like this
from abc import ABC
class AnyData(ABC):
…
damantou
- 53
- 6
2
votes
0 answers
Python abstractmethod property - enforce concrete decorator correctly
How can you ensure a concrete class will correctly use @property decorator when overriding an @abstractmethod?
Consider the following abstract class:
class Vehicle(ABC):
def __init__(self):
print(self.gas * 2)
@property
…
Voy
- 5,286
- 1
- 49
- 59