Coverage for /pythoncovmergedfiles/medio/medio/usr/local/lib/python3.8/site-packages/airflow/utils/singleton.py: 67%

1# 

2# Licensed to the Apache Software Foundation (ASF) under one 

3# or more contributor license agreements. See the NOTICE file 

4# distributed with this work for additional information 

5# regarding copyright ownership. The ASF licenses this file 

6# to you under the Apache License, Version 2.0 (the 

7# "License"); you may not use this file except in compliance 

8# with the License. You may obtain a copy of the License at 

9# 

10# http://www.apache.org/licenses/LICENSE-2.0 

11# 

12# Unless required by applicable law or agreed to in writing, 

13# software distributed under the License is distributed on an 

14# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY 

15# KIND, either express or implied. See the License for the 

16# specific language governing permissions and limitations 

17# under the License. 

18from __future__ import annotations 

19 

20from typing import Generic, TypeVar 

21 

22T = TypeVar("T") 

23 

24 

25class Singleton(type, Generic[T]): 

26 """Metaclass that allows to implement singleton pattern.""" 

27 

28 _instances: dict[Singleton[T], T] = {} 

29 

30 def __call__(cls: Singleton[T], *args, **kwargs) -> T: 

31 if cls not in cls._instances: 

32 cls._instances[cls] = super().__call__(*args, **kwargs) 

33 return cls._instances[cls]