====== OOP ======

===== special methods =====
[[https://docs.python.org/3/reference/datamodel.html#special-method-names]]

  * [[https://docs.python.org/3/reference/datamodel.html#object.__new__|__new__]]
  * [[https://docs.python.org/3/reference/datamodel.html#object.__init__|__init__]] - called after the instance has been created by **__new__**
  * [[https://docs.python.org/3/reference/datamodel.html#object.__del__|__del__]] - finalizer: called when the instance is about to be destroyed.
    * It is not guaranteed that __del__() methods are called for objects that still exist when the interpreter exits.
    * **Note**: ''del x'' doesn’t directly call ''x.__del__()'' — the former decrements the reference count for x by one, and the latter is only called when x’s reference count reaches zero. 
  * [[https://docs.python.org/3/reference/datamodel.html#object.__repr__|__repr__]] - Called by the ''repr()'' built-in function to compute the “official” string representation of an object. This is typically used for debugging, so it is important that the representation is information-rich and unambiguous
  * [[https://docs.python.org/3/reference/datamodel.html#object.__str__|__str__]] - Called by ''str(object)'' and the built-in functions ''format()'' and ''print()'' to compute the “informal” or nicely printable string representation of an object.
  * ''__bytes__''
  * ''__format__''
  * ''__lt__ / __le__ / __eq__ / __ne__ / __gt__ / __ge__''
  * ''__hash__''
  * ''__bool__''

===== call super constructor =====
<code python>
class A(object):
    def __init__(self):
        print("world")

class B(A):
    def __init__(self):
        print("hello")
        super().__init__()
</code>

===== singletons =====

<code python>
class MySingleton:
    instance = None

    def __new__(cls, *args, **kwargs):
        if not isinstance(cls.instance, cls):
            cls.instance = object.__new__(cls)
        return cls.instance
</code>

<code python>
class Singleton(type):
    _instances = {}
    def __call__(cls, *args, **kwargs):
        if cls not in cls._instances:
            cls._instances[cls] = super (Singleton,cls).__call__(*args, **kwargs)
        return cls._instances[cls]

class SerialNumber(metaclass=Singleton):

</code>

===== attributes / properties =====

  * **attribute** - direct access to data member of object
  * **property** - properties are methods accessed like attributes. It gives full control on its getter, setter and deleter access.


**delattr(object, name)**
This is a relative of ''setattr()''. The arguments are an object and a string. The string must be the name of one of the object’s attributes. The function deletes the named attribute, provided the object allows it. For example, ''delattr(x, 'foobar')'' is equivalent to ''del x.foobar''. name need not be a Python identifier (see setattr()).


===== Object-like attribute access for nested dictionary =====
  * https://stackoverflow.com/questions/38034377/object-like-attribute-access-for-nested-dictionary
  * https://bobbyhadz.com/blog/python-use-dot-to-access-dictionary
  * https://github.com/frmdstryr/magicattr