feat: replace Digest constants in misctypes.py with cache funcs

Replace`DUMMY_DANDI_ETAG` and `DUMMY_DANDI_ZARR_CHECKSUM`
in `dandi.misctypes` with caching functions. This change
is needed to delay the import of `dandischema.models`
in `dandi.misctypes` and in this package in general

Author: candleindark

dandi/files/bases.py

@@ -175,9 +175,9 @@ class LocalAsset(DandiFile):
 
     @staticmethod
     def _get_dummy_digest() -> Digest:
-        from dandi.misctypes import DUMMY_DANDI_ETAG
+        from dandi.misctypes import get_dummy_dandi_etag
 
-        return DUMMY_DANDI_ETAG
+        return get_dummy_dandi_etag()
 
     @abstractmethod
     def get_digest(self) -> Digest:

dandi/files/zarr.py

@@ -365,9 +365,9 @@ class ZarrAsset(LocalDirectoryAsset[LocalZarrEntry]):
 
     @staticmethod
     def _get_dummy_digest() -> Digest:
-        from dandi.misctypes import DUMMY_DANDI_ZARR_CHECKSUM
+        from dandi.misctypes import get_dummy_dandi_zarr_checksum
 
-        return DUMMY_DANDI_ZARR_CHECKSUM
+        return get_dummy_dandi_zarr_checksum()
 
     @property
     def filetree(self) -> LocalZarrEntry:

dandi/metadata/nwb.py

@@ -13,7 +13,7 @@
 from .. import get_logger
 from ..consts import metadata_all_fields
 from ..files import bids, dandi_file, find_bids_dataset_description
-from ..misctypes import DUMMY_DANDI_ETAG, Digest, LocalReadableFile, Readable
+from ..misctypes import Digest, LocalReadableFile, Readable, get_dummy_dandi_etag
 from ..pynwb_utils import (
     _get_pynwb_metadata,
     get_neurodata_types,
@@ -68,7 +68,7 @@ def get_metadata(
             )
             assert isinstance(df, bids.BIDSAsset)
             if not digest:
-                digest = DUMMY_DANDI_ETAG
+                digest = get_dummy_dandi_etag()
             path_metadata = df.get_metadata(digest=digest)
             meta["bids_version"] = df.get_validation_bids_version()
             # there might be a more elegant way to do this:

dandi/misctypes.py

@@ -11,6 +11,7 @@
 from dataclasses import dataclass
 from datetime import datetime
 from fnmatch import fnmatchcase
+from functools import cache
 import os.path
 from pathlib import Path
 from typing import IO, TypeVar, cast
@@ -54,11 +55,15 @@ def asdict(self) -> dict[DigestType, str]:
 
 #: Placeholder digest used in some situations where a digest is required but
 #: not actually relevant and would be too expensive to calculate
-DUMMY_DANDI_ETAG = Digest(algorithm=DigestType.dandi_etag, value=32 * "d" + "-1")
-DUMMY_DANDI_ZARR_CHECKSUM = Digest(
-    algorithm=DigestType.dandi_zarr_checksum,
-    value=32 * "d" + "-1--1",
-)
+@cache
+def get_dummy_dandi_etag() -> Digest:
+    return Digest(algorithm=DigestType.dandi_etag, value=32 * "d" + "-1")
+
+
+@cache
+def get_dummy_dandi_zarr_checksum() -> Digest:
+    return Digest(algorithm=DigestType.dandi_zarr_checksum, value=32 * "d" + "-1--1")
+
 
 P = TypeVar("P", bound="BasePath")
 

dandi/tests/test_metadata.py

@@ -49,7 +49,7 @@
     species_map,
     timedelta2duration,
 )
-from ..misctypes import DUMMY_DANDI_ETAG
+from ..misctypes import get_dummy_dandi_etag
 from ..utils import ensure_datetime
 
 METADATA_DIR = Path(__file__).with_name("data") / "metadata"
@@ -836,7 +836,9 @@ def test_ndtypes(ndtypes, asset_dict):
 def test_nwb2asset(simple2_nwb: Path) -> None:
     # Classes with ANY_AWARE_DATETIME fields need to be constructed with
     # model_construct()
-    assert nwb2asset(simple2_nwb, digest=DUMMY_DANDI_ETAG) == BareAsset.model_construct(
+    assert nwb2asset(
+        simple2_nwb, digest=get_dummy_dandi_etag()
+    ) == BareAsset.model_construct(
         schemaKey="Asset",
         schemaVersion=DANDI_SCHEMA_VERSION,
         keywords=["keyword1", "keyword 2"],