dol 0.1.19

Base builtin tools make and transform data object layers (dols).

dol

Base builtin tools make and transform data object layers (dols).

The package is light-weight: Pure python; not third-party dependencies.

Why the name?

• because it's short
• because it's cute
• because it reminds one of "russian dolls" (one way to think of wrappers)
• because we can come up with an acronym the contains "Data Object" in it.

To install: pip install dol

Examples

By store we mean key-value store. This could be files in a filesystem, objects in s3, or a database. Where and how the content is stored should be specified, but StoreInterface offers a dict-like interface to this.

__getitem__ calls: _id_of_key			                    _obj_of_data
__setitem__ calls: _id_of_key		        _data_of_obj
__delitem__ calls: _id_of_key
__iter__    calls:	            _key_of_id

>>> from dol import Store

A Store can be instantiated with no arguments. By default it will make a dict and wrap that.

>>> # Default store: no key or value conversion ################################################
>>> s = Store()
>>> s['foo'] = 33
>>> s['bar'] = 65
>>> assert list(s.items()) == [('foo', 33), ('bar', 65)]
>>> assert list(s.store.items()) == [('foo', 33), ('bar', 65)]  # see that the store contains the same thing

Now let's make stores that have a key and value conversion layer input keys will be upper cased, and output keys lower cased input values (assumed int) will be converted to ascii string, and visa versa

>>>
>>> def test_store(s):
...     s['foo'] = 33  # write 33 to 'foo'
...     assert 'foo' in s  # __contains__ works
...     assert 'no_such_key' not in s  # __nin__ works
...     s['bar'] = 65  # write 65 to 'bar'
...     assert len(s) == 2  # there are indeed two elements
...     assert list(s) == ['foo', 'bar']  # these are the keys
...     assert list(s.keys()) == ['foo', 'bar']  # the keys() method works!
...     assert list(s.values()) == [33, 65]  # the values() method works!
...     assert list(s.items()) == [('foo', 33), ('bar', 65)]  # these are the items
...     assert list(s.store.items()) == [('FOO', '!'), ('BAR', 'A')]  # but note the internal representation
...     assert s.get('foo') == 33  # the get method works
...     assert s.get('no_such_key', 'something') == 'something'  # return a default value
...     del(s['foo'])  # you can delete an item given its key
...     assert len(s) == 1  # see, only one item left!
...     assert list(s.items()) == [('bar', 65)]  # here it is
>>>

We can introduce this conversion layer in several ways.

Here are few...

by subclassing

>>> # by subclassing ###############################################################################
>>> class MyStore(Store):
...     def _id_of_key(self, k):
...         return k.upper()
...     def _key_of_id(self, _id):
...         return _id.lower()
...     def _data_of_obj(self, obj):
...         return chr(obj)
...     def _obj_of_data(self, data):
...         return ord(data)
>>> s = MyStore(store=dict())  # note that you don't need to specify dict(), since it's the default
>>> test_store(s)
>>>

by assigning functions to converters

>>> # by assigning functions to converters ##########################################################
>>> class MyStore(Store):
...     def __init__(self, store, _id_of_key, _key_of_id, _data_of_obj, _obj_of_data):
...         super().__init__(store)
...         self._id_of_key = _id_of_key
...         self._key_of_id = _key_of_id
...         self._data_of_obj = _data_of_obj
...         self._obj_of_data = _obj_of_data
...
>>> s = MyStore(dict(),
...             _id_of_key=lambda k: k.upper(),
...             _key_of_id=lambda _id: _id.lower(),
...             _data_of_obj=lambda obj: chr(obj),
...             _obj_of_data=lambda data: ord(data))
>>> test_store(s)
>>>

using a Mixin class

>>> # using a Mixin class #############################################################################
>>> class Mixin:
...     def _id_of_key(self, k):
...         return k.upper()
...     def _key_of_id(self, _id):
...         return _id.lower()
...     def _data_of_obj(self, obj):
...         return chr(obj)
...     def _obj_of_data(self, data):
...         return ord(data)
...
>>> class MyStore(Mixin, Store):  # note that the Mixin must come before Store in the mro
...     pass
...
>>> s = MyStore()  # no dict()? No, because default anyway
>>> test_store(s)

adding wrapper methods to an already made Store instance

>>> # adding wrapper methods to an already made Store instance #########################################
>>> s = Store(dict())
>>> s._id_of_key=lambda k: k.upper()
>>> s._key_of_id=lambda _id: _id.lower()
>>> s._data_of_obj=lambda obj: chr(obj)
>>> s._obj_of_data=lambda data: ord(data)
>>> test_store(s)