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fix(zarr-metadata): accept the generic time unit in v2 time dtypes #422

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fix(zarr-metadata): accept the generic time unit in v2 time dtypes #422

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fix(zarr-metadata): accept the generic time unit in v2 time dtypes
d-v-b Oct 29, 2026
282d2fb
docs(zarr-metadata): changelog fragment for #422
d-v-b Oct 29, 2026
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1 change: 1 addition & 0 deletions packages/zarr-metadata/changes/422.bugfix.md
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The Zarr format 2 time dtypes accept the generic time unit in brackets — `<M8[generic]`, or `<m8[2generic]` with a scale — the spellings zarr-python writes for a NumPy generic-unit time dtype. A unit is still required: the unitless `<M8` stays refused, as the v2 spec demands.
3 changes: 2 additions & 1 deletion packages/zarr-metadata/src/zarr_metadata/_numpy.py
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Expand Up @@ -24,8 +24,9 @@
"ps",
"fs",
"as",
"generic",
)
"""The units NumPy accepts for a datetime64 or timedelta64 (https://numpy.org/doc/stable/reference/arrays.datetime.html#datetime-units). The v3 types also accept `"generic"`."""
"""The units NumPy accepts for a datetime64 or timedelta64 (https://numpy.org/doc/stable/reference/arrays.datetime.html#datetime-units), and `"generic"`, NumPy's unit-less unit, which NumPy parses in brackets (`<M8[generic]`) though its own `dtype.str` omits it. The v2 spec's unit table does not list `generic`, but zarr-python writes it (zarr-developers/zarr-python#4580)."""

NUMPY_TIME_MAX_SCALE_FACTOR: Final = 2**31 - 1
"""The largest `scale_factor` that numpy stores, because the field is a signed int32."""
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2 changes: 1 addition & 1 deletion packages/zarr-metadata/src/zarr_metadata/v3/data_type/_numpy_time.py
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Expand Up @@ -14,7 +14,7 @@
]
"""The time unit codes of the numpy time types, `numpy.datetime64` and `numpy.timedelta64`."""

NUMPY_TIME_UNIT: Final = (*NUMPY_TIME_UNITS, "generic")
NUMPY_TIME_UNIT: Final = NUMPY_TIME_UNITS
"""Runtime tuple of the permitted `numpy.timedelta64`/`numpy.datetime64` unit strings."""

numpy_time_storage: Final = multi_byte
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2 changes: 2 additions & 0 deletions packages/zarr-metadata/tests/v2/test_data_types.py
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Expand Up @@ -59,7 +59,9 @@ def _read(value: object) -> tuple[type, list[tuple[Loc, str]]]:
("<M8[ns]", "datetime64", "<M8[ns]"),
(">M8[10s]", "datetime64", ">M8[10s]"),
("<M8[μs]", "datetime64", "<M8[us]"),
("<M8[generic]", "datetime64", "<M8[generic]"),
("<m8[D]", "timedelta64", "<m8[D]"),
(">m8[2generic]", "timedelta64", ">m8[2generic]"),
([["x", "<f4"], ["y", "<i4", [2]]], "struct", (("x", "<f4"), ("y", "<i4", (2,)))),
([["r", "|u1"], ["s", [["t", "<f4"]]]], "struct", (("r", "|u1"), ("s", (("t", "<f4"),)))),
# NumPy names the padding fields of an aligned struct "", and zarr 2.x writes them.
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