Coverage for /pythoncovmergedfiles/medio/medio/src/airflow/airflow/utils/singleton.py: 67%
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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
20from typing import Generic, TypeVar
22T = TypeVar("T")
25class Singleton(type, Generic[T]):
26 """Metaclass that allows to implement singleton pattern."""
28 _instances: dict[Singleton[T], T] = {}
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]