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Frozen dict cannot use flatten, unflatten, subset or filter

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  • #614 di @itzzdev09 — integrata

Valutazione

Difficoltà
3/5
Tempo stimato
1-2 giorni
Idoneità per principianti
78/100
Tipo di issue
Bug
Chiarezza
Specificata chiaramente
Stato di attività
Attiva
Stack tecnologico
python
Ambito
backend

Direzione di ricerca

Start with core/clone.py, especially the empty=True path and BaseDict.deepcopy, then inspect the affected call sites in core/filter.py, core/flatten.py, core/invert.py, core/subset.py, and core/unflatten.py. Done means these derivation methods work on frozen dictionaries without modifying the source, while ordinary clone() remains frozen.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

Summary

flatten, unflatten, subset and filter raise TypeError on a frozen dict, although all four are documented as returning a new dict and none of them mutate the source.

from benedict import benedict

d = benedict({"a": 1, "nested": {"x": 1}}).freeze()

d.flatten()
# TypeError: 'benedict' object is frozen and cannot be modified.

clone, keypaths, search, match, groupby and to_json all work fine on the same frozen dict, so the behaviour is inconsistent — freezing blocks some read-only derivations but not others.

method mutates source on a frozen dict
clone no works
keypaths, search, match, groupby, to_json no works
flatten no TypeError
unflatten no TypeError
subset no TypeError
filter no TypeError

Cause

All four build their result with clone(d, empty=True). In benedict/core/clone.py:

d = copy.deepcopy(obj, memo)
if empty and isinstance(d, MutableMapping):
    d.clear()
return d

BaseDict.__deepcopy__ deliberately carries the frozen flag over:

if self._frozen:
    obj.freeze()

so the deep copy is frozen, and the following clear() hits _check_frozen() and raises. The exception therefore comes from the throwaway internal copy rather than from the dict the caller passed in — which is why the error message is a little misleading too.

Plain clone() is unaffected because it never clears.

Affected call sites: core/filter.py (x2), core/flatten.py, core/invert.py, core/subset.py, core/unflatten.py.

Expected

Freezing is meant to prevent modification of the dict. Deriving a new dict from it is a read, so it should be allowed, the way clone() already is. This matters for the obvious use of freeze() — holding an immutable config and taking subsets or flattened views of it.

Notes

Propagating frozen through __deepcopy__ looks intentional and worth keeping: a full clone() of an immutable dict staying immutable is reasonable. The issue is only the empty=True path, where the copy is emptied and refilled, so the source's frozen state has no meaning.

Reproduced on main at e9641ec, Python 3.12. PR follows.

Lingua principale
Python
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