make lh5 types and exceptions picklable

src/lgdo/lh5/exceptions.py

@@ -16,6 +16,9 @@ def __str__(self) -> str:
             + super().__str__()
         )
 
+    def __reduce__(self) -> tuple:  # for pickling.
+        return self.__class__, (*self.args, self.file, self.obj)
+
 
 class LH5EncodeError(Exception):
     def __init__(
@@ -32,3 +35,6 @@ def __str__(self) -> str:
             f"while writing object {self.group}/{self.name} to file {self.file}: "
             + super().__str__()
         )
+
+    def __reduce__(self) -> tuple:  # for pickling.
+        return self.__class__, (*self.args, self.file, self.group, self.name)

src/lgdo/types/histogram.py

@@ -418,13 +418,18 @@ def fill(self, data, w: NDArray = None, keys: Sequence[str] = None) -> None:
 
     def __setitem__(self, name: str, obj: LGDO) -> None:
         # do not allow for new attributes on this
-        msg = "histogram fields cannot be mutated"
-        raise TypeError(msg)
+        known_keys = ("binning", "weights", "isdensity")
+        if name in known_keys and not dict.__contains__(self, name):
+            # but allow initialization while unpickling (after __init__() this is unreachable)
+            dict.__setitem__(self, name, obj)
+        else:
+            msg = "histogram fields cannot be mutated "
+            raise TypeError(msg)
 
     def __getattr__(self, name: str) -> None:
         # do not allow for new attributes on this
         msg = "histogram fields cannot be mutated"
-        raise TypeError(msg)
+        raise AttributeError(msg)
 
     def add_field(self, name: str | int, obj: LGDO) -> None:  # noqa: ARG002
         """

src/lgdo/types/lgdo.py

@@ -11,6 +11,12 @@
 class LGDO(ABC):
     """Abstract base class representing a LEGEND Data Object (LGDO)."""
 
+    def __new__(cls, *_args, **_kwargs):
+        # allow for (un-)pickling LGDO objects.
+        obj = super().__new__(cls)
+        obj.attrs = {}
+        return obj
+
     @abstractmethod
     def __init__(self, attrs: dict[str, Any] | None = None) -> None:
         self.attrs = {} if attrs is None else dict(attrs)

src/lgdo/types/table.py

@@ -41,6 +41,12 @@ class Table(Struct):
     :meth:`__len__` to access valid data, which returns the ``size`` attribute.
     """
 
+    def __new__(cls, *args, **kwargs):
+        # allow for (un-)pickling LGDO objects.
+        obj = super().__new__(cls, *args, **kwargs)
+        obj.size = None
+        return obj
+
     def __init__(
         self,
         col_dict: Mapping[str, LGDO] | pd.DataFrame | ak.Array | None = None,

tests/lh5/test_exceptions.py

@@ -0,0 +1,17 @@
+from __future__ import annotations
+
+import pickle
+
+from lgdo.lh5.exceptions import LH5DecodeError, LH5EncodeError
+
+
+def test_pickle():
+    # test (un-)pickling of LH5 exceptions; e.g. for multiprocessing use.
+
+    ex = LH5EncodeError("message", "file", "group", "name")
+    ex = pickle.loads(pickle.dumps(ex))
+    assert isinstance(ex, LH5EncodeError)
+
+    ex = LH5DecodeError("message", "file", "obj")
+    ex = pickle.loads(pickle.dumps(ex))
+    assert isinstance(ex, LH5DecodeError)

tests/types/test_array.py

@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+import pickle
+
 import awkward as ak
 import numpy as np
 import pandas as pd
@@ -61,3 +63,14 @@ def test_view():
 
     with pytest.raises(ValueError):
         a.view_as("ak", with_units=True)
+
+
+def test_pickle():
+    obj = Array(nda=np.array([1, 2, 3, 4]))
+    obj.attrs["attr1"] = 1
+
+    ex = pickle.loads(pickle.dumps(obj))
+    assert isinstance(ex, Array)
+    assert ex.attrs["attr1"] == 1
+    assert ex.attrs["datatype"] == obj.attrs["datatype"]
+    assert np.all(ex.nda == np.array([1, 2, 3, 4]))

tests/types/test_encoded.py

@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+import pickle
+
 import awkward as ak
 import awkward_pandas as akpd
 import numpy as np
@@ -285,3 +287,51 @@ def test_aoeesa_view_as():
 
     with pytest.raises(TypeError):
         df = voev.view_as("np")
+
+
+def test_aoeesa_pickle():
+    obj = ArrayOfEncodedEqualSizedArrays(
+        encoded_data=VectorOfVectors(
+            flattened_data=Array(nda=np.array([1, 2, 3, 4, 5, 2, 4, 8, 9, 7, 5, 3, 1])),
+            cumulative_length=Array(nda=np.array([2, 5, 6, 10, 13])),
+        ),
+        decoded_size=99,
+    )
+
+    ex = pickle.loads(pickle.dumps(obj))
+
+    desired = [
+        [1, 2],
+        [3, 4, 5],
+        [2],
+        [4, 8, 9, 7],
+        [5, 3, 1],
+    ]
+
+    for i, v in enumerate(ex):
+        assert np.array_equal(v, desired[i])
+
+
+def test_voev_pickle():
+    obj = VectorOfEncodedVectors(
+        encoded_data=VectorOfVectors(
+            flattened_data=Array(nda=np.array([1, 2, 3, 4, 5, 2, 4, 8, 9, 7, 5, 3, 1])),
+            cumulative_length=Array(nda=np.array([2, 5, 6, 10, 13])),
+        ),
+        decoded_size=Array(shape=5, fill_val=6),
+        attrs={"units": "s"},
+    )
+
+    ex = pickle.loads(pickle.dumps(obj))
+
+    desired = [
+        [1, 2],
+        [3, 4, 5],
+        [2],
+        [4, 8, 9, 7],
+        [5, 3, 1],
+    ]
+
+    for i, (v, s) in enumerate(ex):
+        assert np.array_equal(v, desired[i])
+        assert s == 6

tests/types/test_histogram.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import logging
+import pickle
 
 import hist
 import numpy as np
@@ -266,7 +267,7 @@ def test_view_as_np():
 def test_not_like_table():
     h = Histogram(np.array([1, 1]), (np.array([0, 1, 2]),))
     assert h.form_datatype() == "struct{binning,weights,isdensity}"
-    with pytest.raises(TypeError):
+    with pytest.raises(AttributeError):
         x = h.x  # noqa: F841
     with pytest.raises(TypeError):
         h["x"] = Scalar(1.0)
@@ -392,3 +393,14 @@ def test_histogram_fill():
 
     with pytest.raises(ValueError, match="data must be"):
         h.fill(np.ones(shape=(5, 5)))
+
+
+def test_pickle():
+    obj = Histogram(np.array([1, 1]), (Histogram.Axis.from_range_edges([0, 1, 2]),))
+    obj.attrs["attr1"] = 1
+
+    ex = pickle.loads(pickle.dumps(obj))
+    assert isinstance(ex, Histogram)
+    assert ex.attrs["attr1"] == 1
+    assert ex.attrs["datatype"] == obj.attrs["datatype"]
+    assert np.all(ex.weights == obj.weights)

tests/types/test_scalar.py

@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+import pickle
+
 import pytest
 
 import lgdo
@@ -33,3 +35,14 @@ def test_getattrs():
 
 def test_equality():
     assert lgdo.Scalar(value=42) == lgdo.Scalar(value=42)
+
+
+def test_pickle():
+    obj = lgdo.Scalar(value=10)
+    obj.attrs["attr1"] = 1
+
+    ex = pickle.loads(pickle.dumps(obj))
+    assert isinstance(ex, lgdo.Scalar)
+    assert ex.attrs["attr1"] == 1
+    assert ex.attrs["datatype"] == obj.attrs["datatype"]
+    assert ex.value == 10

tests/types/test_struct.py

@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+import pickle
+
 import pytest
 
 import lgdo
@@ -78,3 +80,15 @@ def test_remove_field():
 
     struct.remove_field("array1", delete=True)
     assert list(struct.keys()) == []
+
+
+def test_pickle():
+    obj_dict = {"scalar1": lgdo.Scalar(value=10)}
+    attrs = {"attr1": 1}
+    struct = lgdo.Struct(obj_dict=obj_dict, attrs=attrs)
+
+    ex = pickle.loads(pickle.dumps(struct))
+    assert isinstance(ex, lgdo.Struct)
+    assert ex.attrs["attr1"] == 1
+    assert ex.attrs["datatype"] == struct.attrs["datatype"]
+    assert ex["scalar1"].value == 10

tests/types/test_table.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import pickle
 import warnings
 
 import awkward as ak
@@ -221,3 +222,20 @@ def test_remove_column():
 
     tbl.remove_column("c")
     assert list(tbl.keys()) == ["b"]
+
+
+def test_pickle():
+    col_dict = {
+        "a": lgdo.Array(nda=np.array([1, 2, 3, 4])),
+        "b": lgdo.Array(nda=np.array([5, 6, 7, 8])),
+        "c": lgdo.Array(nda=np.array([9, 10, 11, 12])),
+    }
+    obj = Table(col_dict=col_dict)
+    obj.attrs["attr1"] = 1
+
+    ex = pickle.loads(pickle.dumps(obj))
+    assert isinstance(ex, Table)
+    assert ex.attrs["attr1"] == 1
+    assert ex.attrs["datatype"] == obj.attrs["datatype"]
+    for key, val in col_dict.items():
+        assert ex[key] == val

tests/types/test_vectorofvectors.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import copy
+import pickle
 from collections import namedtuple
 
 import awkward as ak
@@ -441,3 +442,19 @@ def test_lh5_iterator_view_as(lgnd_test_data):
 
     for obj, _, _ in it:
         assert ak.is_valid(obj.view_as("ak"))
+
+
+def test_pickle(testvov):
+    obj = testvov.v2d
+    ex = pickle.loads(pickle.dumps(obj))
+
+    desired = [
+        np.array([1, 2]),
+        np.array([3, 4, 5]),
+        np.array([2]),
+        np.array([4, 8, 9, 7]),
+        np.array([5, 3, 1]),
+    ]
+
+    for i in range(len(desired)):
+        assert np.array_equal(desired[i], ex[i])