python - Define a constructor in full classmethod class -

let's have following class :

class context:      element_list = []      @classmethod     def add(cls, element):         cls.element_list.append(element)      @classmethod     def remove(cls, element):         cls.element_list.remove(cls.element_list.index(element)) 

this class near of singleton class. objective update element_list attribute anywhere in program without passing context instance parameter of functions.

pycharm signals me should define __init__ method. not want create 2 different instances of class. thinking creating dummy __init__ method :

def __init__(self):     raise notimplementederror("this class should not initialized") 

the question(s) (are) : should define __init__ method ? if yes how ? instead of using classmethod implementation should use singleton class (see: is there simple, elegant way define singletons?)

1. the __init__ method not mandatory. should define __init__ method if want pass state instance being initialized. looking @ code snippet provided, doesn't seem case.

2. there few ways (hacks) implement singleton pattern in python:

   • check out borg pattern
   • see stack overflow thread on creating singleton in python

   however, think methods aren't pythonic , should avoided majority of cases.

   as others have said, use python modules. python modules 1 of awesome features of python programming language. can have state (variables), behaviors (functions) , within 1 python process execution, a module loaded once.

   this means that, in directory structure like:

   . ├── bar.py ├── foo.py ├── main.py └── singleton.py 

   you do:

   # file: singleton.py element_list = [] 

   and rest of application import , use it:

   # file: foo.py import singleton  def foo():     # ... complex computations ...     singleton.element_list.append('baz') 

   ---

   # file: bar.py import singleton  def bar():     # ... more complex things ...     if 'baz' in singleton.element_list:         print('baz') 

   ---

   # file: main.py import foo import bar  foo.foo() bar.bar() # outputs: 'baz' 

   as can see, besides being simple , more elegant, using module gives usual list utilities interface (for instance, singleton.element_list[1:] or singleton.element_list + ['my', 'other', 'list'], , on). if wanted way, have implement other classmethods.