py-singleton

Singleton pattern for python 2 & 3.

Install

pip install py-singleton

Test

in the root folder, run pytest:

pytest

Dependencies

None

unit test needs pytest.

API

• Apply class decorator singleton to any class;

• Expected behaviors:

  • class can be instantiated as usual, but only one instance is created;
  • apis to access the class instance:

    @singleton
    class Server(object):
      pass
  
    srv = Server()

  or

    srv = Server.instance()

  • the function _init_() of decorated class will be called once and only once when the instance is created.

Example

from py_singleton import singleton

    @singleton
    class A(object):
        count = 0
        def __init__(self):
            A.count += 1

    a1 = A()
    a2 = A()
    a3 = A.instance()

    assert A.count == 1
    assert a1 is a2
    assert a1 is a3

Limitation

For best performance, the code to create instance is not thread-safe, however, after the instance is created it should be safe for multi-threading.

It is recommended to call instance() once during the initial phrase of your app in a single thread.