Add NoCopyMixin and NoCopyDict to ease intentionally mutable model pr…

…ivate attributes

Signed-off-by: Jacob Hayes <jacob.r.hayes@gmail.com>

src/arti/backends/memory.py

@@ -3,17 +3,15 @@
 from collections import defaultdict
 from collections.abc import Iterator
 from contextlib import contextmanager
-from typing import Any, TypeVar
 
 from pydantic import PrivateAttr
 
 from arti.artifacts import Artifact
 from arti.backends import Backend
 from arti.fingerprints import Fingerprint
+from arti.internal.utils import NoCopyMixin
 from arti.storage import AnyStorage, InputFingerprints, StoragePartition, StoragePartitions
 
-_Self = TypeVar("_Self")
-
 
 def _ensure_fingerprinted(partitions: StoragePartitions) -> Iterator[StoragePartition]:
     for partition in partitions:
@@ -24,7 +22,7 @@ def _ensure_fingerprinted(partitions: StoragePartitions) -> Iterator[StoragePart
 _StoragePartitions = dict[AnyStorage, set[StoragePartition]]
 
 
-class _NoCopyContainer:
+class _NoCopyContainer(NoCopyMixin):
     """Container for MemoryBackend data that bypasses (deep)copying.
 
     The MemoryBackend is *intended* to be stateful, like a connection to an external database in
@@ -45,12 +43,6 @@ def __init__(self) -> None:
         self.graph_tags: dict[str, dict[str, Fingerprint]] = defaultdict(dict)
         self.storage_partitions: _StoragePartitions = defaultdict(set[StoragePartition])
 
-    def __copy__(self: _Self) -> _Self:
-        return self  # pragma: no cover
-
-    def __deepcopy__(self: _Self, memo: Any) -> _Self:
-        return self  # pragma: no cover
-
 
 class MemoryBackend(Backend):
     _container: _NoCopyContainer = PrivateAttr(default_factory=_NoCopyContainer)

src/arti/internal/utils.py

@@ -326,6 +326,27 @@ def qname(val: Union[object, type]) -> str:
     return type(val).__qualname__
 
 
+_Self = TypeVar("_Self")
+
+
+class NoCopyMixin:
+    """Mixin to bypass (deep)copying.
+
+    This is useful for objects that are *intended* to be stateful and preserved, despite usually
+    preferring immutable data structures and Pydantic models, which (deep)copy often.
+    """
+
+    def __copy__(self: _Self) -> _Self:
+        return self  # pragma: no cover
+
+    def __deepcopy__(self: _Self, memo: Any) -> _Self:
+        return self  # pragma: no cover
+
+
+class NoCopyDict(dict[_K, _V], NoCopyMixin):
+    pass
+
+
 _K_str = TypeVar("_K_str")