singleton.py

''' Singleton decorator to restricts a class to a single instance

    Copyright (c) 2025 Harm Lammers
    
    The singleton function was taken from (only adding a docstring) 
    https://github.com/peterhinch/micropython-samples/tree/master/functor_singleton copyright (c) Peter Hinch, published under MIT licence

    MIT licence:

    Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the
    "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish,
    distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to
    the following conditions:

    The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
    CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
    SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
'''

def singleton(cls):
    ''' Decorator function which restricts a class to a single instance: creates the instance only on first-time instantiation and return that
    instance on each consecutive instantiation
    '''
    instance = None
    def get_instance(*args, **kwargs):
        nonlocal instance
        if instance is None:
            instance = cls(*args, **kwargs)
        return instance
    return get_instance