datahold - Wrap common mutable datastructures for inheritance with modification

Content

HoldABC

class HoldABC(abc.ABC):
    @abc.abstractmethod
    def __init__(self, *args, **kwargs) -> None: ...

    @property
    @abc.abstractmethod
    def data(self): ...

    

HoldList

To understand the class HoldList here the beginning of its code:

class HoldList(HoldABC, collections.abc.MutableSequence):

    data: list

    @functools.wraps(list.__add__)
    def __add__(self, *args, **kwargs):
        data = self.data
        ans = data.__add__(*args, **kwargs)
        self.data = data
        return ans

    

The following methods are defined this way: __add__, __contains__, __delitem__, __eq__, __format__, __ge__, __getitem__, __gt__, __hash__, __iadd__, __imul__, __iter__, __le__, __len__, __lt__, __mul__, __repr__, __reversed__, __rmul__, __setitem__, __str__, append, clear, copy, count, extend, index, insert, pop, remove, reverse, sort.

The only function present in list and absent in HoldList is __class_getitem__

We can use HoldList as a parent for a list-like class. It is necessary to implement in the subclass:

• a property named data
• the __init__ magic method

This allows the creation of a list-like class with modified behavior with only minimal effort. To enhance performance, we can overwrite some of the methods.

HoldDict

Just like HoldList but for dict... It inherits from HoldABC and collections.abc.MutableMapping. The following methods are implemented: __contains__, __delitem__, __eq__, __format__, __ge__, __getitem__, __gt__, __hash__, __ior__, __iter__, __le__, __len__, __lt__, __or__, __repr__, __reversed__, __ror__, __setitem__, __str__, clear, copy, get, items, keys, pop, popitem, setdefault, update, values.

The classmethods __class_getitem__ and fromkeys are not implemented.

HoldSet

Just like HoldSet but for set... It inherits from HoldABC and collections.abc.MutableSet. The following methods are implemented: __and__, __contains__, __eq__, __format__, __ge__, __gt__, __hash__, __iand__, __ior__, __isub__, __iter__, __ixor__, __le__, __len__, __lt__, __or__, __rand__, __repr__, __ror__, __rsub__, __rxor__, __str__, __sub__, __xor__, add, clear, copy, difference, difference_update, discard, intersection, intersection_update, isdisjoint, issubset, issuperset, pop, remove, symmetric_difference, symmetric_difference_update, union, update.

The classmethod __class_getitem__ is not implemented.

OkayABC

A common abc for OkayList, OkayDict, and OkaySet. Child of Protected (see protectedclasses), Scaevola (see scaevola), and HoldABC. It implements common sense overwrites for some methods. For example:

• all methods that cannot actually change the underlying object are now bound to _data instead of data
• __bool__ is implemented as bool(self._data) because neither list, dict, nor set have a __bool__ method defined.
• __hash__ raises now a more fitting exception
• the comparison operations are overwritten:
  • __eq__ returns self._data == type(self._data)(other)
  • __ne__ negates __eq__
  • __ge__ returns type(self)(other) <= self (inherited from scaevola.Scaevola)
  • __gt__ returns not (self == other) and (self >= other)
  • __lt__ returns not (self == other) and (self <= other)
  • __le__ returns self._data <= type(self)(other)._data
• modify __eq__ or __le__ as needed to change the behavior of the other comparison methods

OkayList

This class inherits from HoldList and OkayABC. It implements a data property that binds a variable _data.

@property
def data(self, /):
    return list(self._data)

@data.setter
def data(self, values, /):
    self._data = list(values)

@data.deleter
def data(self, /):
    self._data = list()

    

Based on that, it implements common sense methods. For example:

• all methods that returned a list before now return OkayList (type adapts to further inheritance)
• __init__ allows now to set data immediately

OkayDict

A subclass of HoldDict with common sense implementations for further inheritance just like OkayList for HoldList.

OkaySet

A subclass of HoldSet with common sense implementations for further inheritance just like OkayList for HoldList.

Installation

To install datahold, you can use pip. Open your terminal and run:

pip install datahold

License

This project is licensed under the MIT License.

Links

• Documentation
• Download
• Source

Credits

• Author: Johannes
• Email: johannes-programming@mailfence.com