Misc edge cases and fragilities

[thorwhalen]

To collect misc edge cases and fragilities that we'd like to address at some point.

[thorwhalen]

__missing__ handling and partial or signature strangeness?

See how we do add_prefix_filtering now:

dol/dol/paths.py

Line 840 in dfcffa2

def add_prefix_filtering(store=None, *, relativize_prefix: bool = False):

The unnecessary conditional clause jumps out, right?

You'd think we can do some partial trick here, something like:

def _prefix_filter(store, prefix: str, *, relativize_prefix: bool = False):
    """Filter the store to have only keys that start with prefix"""
    store = filt_iter(store, filt=partial(_startswith, prefix=prefix))
    if relativize_prefix:
        store = prefixless_view(store, prefix=prefix)
    return store

@store_decorator
def add_prefix_filtering(store=None, *, relativize_prefix: bool = False):
    """Add prefix filtering to a store.

    >>> d = {'a/b': 1, 'a/c': 2, 'd/e': 3, 'f': 4}
    >>> s = add_prefix_filtering(d)
    >>> assert s['a/'] == {'a/b': 1, 'a/c': 2}

    Demo usage on a `Mapping` type:

    >>> from collections import UserDict
    >>> D = add_prefix_filtering(UserDict)
    >>> s = D(d)
    >>> assert s['a/'] == {'a/b': 1, 'a/c': 2}

    """
    __prefix_filter = partial(_prefix_filter, relativize_prefix=relativize_prefix)
    return add_missing_key_handling(store, missing_key_callback=__prefix_filter)

But that brings up this error:

______ [doctest] dol.paths.add_prefix_filtering ______
368 Add prefix filtering to a store.
369 
370     >>> d = {'a/b': 1, 'a/c': 2, 'd/e': 3, 'f': 4}
371     >>> s = add_prefix_filtering(d)
372     >>> assert s['a/'] == {'a/b': 1, 'a/c': 2}
UNEXPECTED EXCEPTION: TypeError("_prefix_filter() missing 1 required positional argument: 'prefix'")
Traceback (most recent call last):
  File "/Users/thorwhalen/Dropbox/py/proj/i/dol/dol/base.py", line 617, in __getitem__
    data = self.store[_id]
KeyError: 'a/'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "/Users/thorwhalen/.pyenv/versions/3.10.8/lib/python3.10/doctest.py", line 1350, in __run
    exec(compile(example.source, filename, "single",
  File "<doctest dol.paths.add_prefix_filtering[2]>", line 1, in <module>
  File "/Users/thorwhalen/Dropbox/py/proj/i/dol/dol/base.py", line 619, in __getitem__
    data = self.__missing__(k)
TypeError: _prefix_filter() missing 1 required positional argument: 'prefix'

Seems like it's something fragile about the way we structured the wrapper here, and/or something to do with the signature of __prefix_filter?

[thorwhalen]

value_wrap

The codec_wrap function in dol.kv_codecs doesn't assign a signature that is consistent with the way the factory should be called.
At the time of writing this, _codec_wrap code shows that the encoder and decoder are parametrized with keyword only, yet the signature shows position-or-keyword.

Also, we'd like to be able to make things like below (using normal functions, not attached to a class) work (it doesn't now).
That is, we'd like to be able to specify any two encoder and decoder factories, and get a "merged" factory, that will make a Codec instance with the parametrized encoder and decoder:

@_add_default_codecs
class ValueCodecs(CodecCollection):

    ....

    single_nested_value: Codec[KT, Dict[KT, VT]] = value_wrap(
        _single_nest_in_dict, _single_itemgetter
    )
    tuple_of_dict: Codec[Iterable[VT], Dict[KT, VT]] = value_wrap(
        _nest_in_dict, _multiple_itemgetter
    )
    

    def _single_itemgetter(key):
        return itemgetter(key)


    def _multiple_itemgetter(keys):
        return itemgetter(*keys)


    def _single_nest_in_dict(key):
        return partial(single_nest_in_dict, key)


    def _nest_in_dict(keys):
        return partial(nest_in_dict, keys)