Fix null list of structs being read and written as an empty list#3834

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Fix null list of structs being read and written as an empty list #3834

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69af7ae
Fix null list of structs being read and written as an empty list
slachiewicz Aug 23, 2026
1ee2f40
Keep the list rebuild for renamed fields, not for arrow#38809
slachiewicz Aug 23, 2026
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9 changes: 6 additions & 3 deletions pyiceberg/io/pyarrow.py
View file
Open in desktop
Original file line numberDiff line numberDiff line change
Expand Up@@ -2073,9 +2073,12 @@ def list(self, list_type: ListType, list_array: pa.Array | None, value_array: pa
if isinstance(list_array, (pa.ListArray, pa.LargeListArray, pa.FixedSizeListArray)) and value_array is not None:
list_initializer = pa.large_list if isinstance(list_array, pa.LargeListArray) else pa.list_
if isinstance(value_array, pa.StructArray):
# This can be removed once this has been fixed:
# https://github.com/apache/arrow/issues/38809
list_array = pa.LargeListArray.from_arrays(list_array.offsets, value_array)
# Rebuilding is what applies the projection to the element struct. A plain
# cast would not do: Iceberg renames by field-id, while cast matches the
# element fields by name and would silently null out any renamed one. The
# mask has to be carried over because the offsets buffer alone cannot
# express a null list, only an empty one.
list_array = pa.LargeListArray.from_arrays(list_array.offsets, value_array, mask=list_array.is_null())
value_array = self._cast_if_needed(list_type.element_field, value_array)
arrow_field = list_initializer(self._construct_field(list_type.element_field, value_array.type))
return list_array.cast(arrow_field)
Expand Down
5 changes: 1 addition & 4 deletions tests/integration/test_reads.py
View file
Open in desktop
Original file line numberDiff line numberDiff line change
Expand Up@@ -994,10 +994,7 @@ def test_null_list_and_map(catalog: Catalog) -> None:
arrow_table = table_test_empty_list_and_map.scan().to_arrow()
assert arrow_table["col_list"].to_pylist() == [None, []]
assert arrow_table["col_map"].to_pylist() == [None, []]
# This should be:
# assert arrow_table["col_list_with_struct"].to_pylist() == [None, [{'test': 1}]]
# Once https://github.com/apache/arrow/issues/38809 has been fixed
assert arrow_table["col_list_with_struct"].to_pylist() == [[], [{"test": 1}]]
assert arrow_table["col_list_with_struct"].to_pylist() == [None, [{"test": 1}]]


@pytest.mark.integration
Expand Down
71 changes: 71 additions & 0 deletions tests/io/test_pyarrow.py
View file
Open in desktop
Original file line numberDiff line numberDiff line change
Expand Up@@ -3210,6 +3210,77 @@ def test__to_requested_schema_float_promotion(
assert result.column(0).to_pylist() == [1.5, 2.25, 3.0, None]


def test__to_requested_schema_null_list_of_structs() -> None:
"""Test that a null list survives the write path when its element is a struct."""
requested_schema = Schema(
NestedField(
1,
"col_list_with_struct",
ListType(11, StructType(NestedField(111, "test", IntegerType(), required=False)), element_required=False),
required=False,
),
NestedField(2, "col_list", ListType(21, IntegerType(), element_required=False), required=False),
)
file_schema = requested_schema

arrow_schema = pa.schema(
[
pa.field("col_list_with_struct", pa.list_(pa.struct([pa.field("test", pa.int32())]))),
pa.field("col_list", pa.list_(pa.int32())),
]
)
batch = pa.RecordBatch.from_arrays(
[
pa.array([[{"test": 1}], [], None], type=arrow_schema.field(0).type),
pa.array([[1], [], None], type=arrow_schema.field(1).type),
],
schema=arrow_schema,
)

result = _to_requested_schema(
requested_schema, file_schema, batch, downcast_ns_timestamp_to_us=False, include_field_ids=False
)

# A null list and an empty list are different values, and only the struct-element
# case ever collapsed the former into the latter.
assert result.column(0).to_pylist() == [[{"test": 1}], [], None]
assert result.column(1).to_pylist() == [[1], [], None]


def test__to_requested_schema_renamed_field_in_list_of_structs() -> None:
"""Test that a field renamed inside a list element keeps its values."""
file_schema = Schema(
NestedField(
1,
"col",
ListType(11, StructType(NestedField(111, "before", IntegerType(), required=False)), element_required=False),
required=False,
),
)
requested_schema = Schema(
NestedField(
1,
"col",
ListType(11, StructType(NestedField(111, "after", IntegerType(), required=False)), element_required=False),
required=False,
),
)

arrow_schema = pa.schema([pa.field("col", pa.list_(pa.struct([pa.field("before", pa.int32())])))])
batch = pa.RecordBatch.from_arrays(
[pa.array([[{"before": 1}], [], None, [{"before": 3}]], type=arrow_schema.field(0).type)],
schema=arrow_schema,
)

result = _to_requested_schema(
requested_schema, file_schema, batch, downcast_ns_timestamp_to_us=False, include_field_ids=False
)

# Rebuilding the list from the projected element array is what carries the rename.
# Casting instead would match the element fields by name and yield nulls throughout.
assert result.column(0).to_pylist() == [[{"after": 1}], [], None, [{"after": 3}]]


def test_pyarrow_file_io_fs_by_scheme_cache() -> None:
# It's better to set up multi-region minio servers for an integration test once `endpoint_url` argument
# becomes available for `resolve_s3_region`
Expand Down
, 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
 blocks\n(function() {\n function addCopyButtons() {\n document.querySelectorAll('pre code').forEach(function(codeBlock) {\n if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;\n codeBlock.parentElement.setAttribute('data-copy-added', 'true');\n \n var btn = document.createElement('button');\n btn.textContent = 'Copy';\n btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';\n btn.onmouseover = function() { this.style.opacity = '1'; };\n btn.onmouseout = function() { this.style.opacity = '0.7'; };\n btn.onclick = function() {\n navigator.clipboard.writeText(codeBlock.textContent).then(function() {\n btn.textContent = 'Copied!';\n setTimeout(function() { btn.textContent = 'Copy'; }, 1500);\n });\n };\n codeBlock.parentElement.style.position = 'relative';\n codeBlock.parentElement.appendChild(btn);\n });\n }\n \n addCopyButtons();\n \n // Re-run on dynamic content\n var observer = new MutationObserver(addCopyButtons);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Add Copy Buttons to Code Blocks");
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

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Fix null list of structs being read and written as an empty list#3834

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Fix null list of structs being read and written as an empty list
#3834
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69af7ae

Fix null list of structs being read and written as an empty list


slachiewicz Aug 23, 2026
1ee2f40

Keep the list rebuild for renamed fields, not for arrow#38809


slachiewicz Aug 23, 2026

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9 changes: 6 additions & 3 deletions
pyiceberg/io/pyarrow.py

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -2073,9 +2073,12 @@ def list(self, list_type: ListType, list_array: pa.Array | None, value_array: pa
 if isinstance(list_array, (pa.ListArray, pa.LargeListArray, pa.FixedSizeListArray)) and value_array is not None:
 list_initializer = pa.large_list if isinstance(list_array, pa.LargeListArray) else pa.list_
 if isinstance(value_array, pa.StructArray):
 # This can be removed once this has been fixed:
 # https://github.com/apache/arrow/issues/38809
 list_array = pa.LargeListArray.from_arrays(list_array.offsets, value_array)
 # Rebuilding is what applies the projection to the element struct. A plain
 # cast would not do: Iceberg renames by field-id, while cast matches the
 # element fields by name and would silently null out any renamed one. The
 # mask has to be carried over because the offsets buffer alone cannot
 # express a null list, only an empty one.
 list_array = pa.LargeListArray.from_arrays(list_array.offsets, value_array, mask=list_array.is_null())
 value_array = self._cast_if_needed(list_type.element_field, value_array)
 arrow_field = list_initializer(self._construct_field(list_type.element_field, value_array.type))
 return list_array.cast(arrow_field)
Expand Down

5 changes: 1 addition & 4 deletions
tests/integration/test_reads.py

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -994,10 +994,7 @@ def test_null_list_and_map(catalog: Catalog) -> None:
 arrow_table = table_test_empty_list_and_map.scan().to_arrow()
 assert arrow_table["col_list"].to_pylist() == [None, []]
 assert arrow_table["col_map"].to_pylist() == [None, []]
 # This should be:
 # assert arrow_table["col_list_with_struct"].to_pylist() == [None, [{'test': 1}]]
 # Once https://github.com/apache/arrow/issues/38809 has been fixed
 assert arrow_table["col_list_with_struct"].to_pylist() == [[], [{"test": 1}]]
 assert arrow_table["col_list_with_struct"].to_pylist() == [None, [{"test": 1}]]


@pytest.mark.integration
Expand Down

71 changes: 71 additions & 0 deletions
tests/io/test_pyarrow.py

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -3210,6 +3210,77 @@ def test__to_requested_schema_float_promotion(
 assert result.column(0).to_pylist() == [1.5, 2.25, 3.0, None]


def test__to_requested_schema_null_list_of_structs() -> None:
 """Test that a null list survives the write path when its element is a struct."""
 requested_schema = Schema(
 NestedField(
 1,
 "col_list_with_struct",
 ListType(11, StructType(NestedField(111, "test", IntegerType(), required=False)), element_required=False),
 required=False,
 ),
 NestedField(2, "col_list", ListType(21, IntegerType(), element_required=False), required=False),
 )
 file_schema = requested_schema

 arrow_schema = pa.schema(
 [
 pa.field("col_list_with_struct", pa.list_(pa.struct([pa.field("test", pa.int32())]))),
 pa.field("col_list", pa.list_(pa.int32())),
 ]
 )
 batch = pa.RecordBatch.from_arrays(
 [
 pa.array([[{"test": 1}], [], None], type=arrow_schema.field(0).type),
 pa.array([[1], [], None], type=arrow_schema.field(1).type),
 ],
 schema=arrow_schema,
 )

 result = _to_requested_schema(
 requested_schema, file_schema, batch, downcast_ns_timestamp_to_us=False, include_field_ids=False
 )

 # A null list and an empty list are different values, and only the struct-element
 # case ever collapsed the former into the latter.
 assert result.column(0).to_pylist() == [[{"test": 1}], [], None]
 assert result.column(1).to_pylist() == [[1], [], None]


def test__to_requested_schema_renamed_field_in_list_of_structs() -> None:
 """Test that a field renamed inside a list element keeps its values."""
 file_schema = Schema(
 NestedField(
 1,
 "col",
 ListType(11, StructType(NestedField(111, "before", IntegerType(), required=False)), element_required=False),
 required=False,
 ),
 )
 requested_schema = Schema(
 NestedField(
 1,
 "col",
 ListType(11, StructType(NestedField(111, "after", IntegerType(), required=False)), element_required=False),
 required=False,
 ),
 )

 arrow_schema = pa.schema([pa.field("col", pa.list_(pa.struct([pa.field("before", pa.int32())])))])
 batch = pa.RecordBatch.from_arrays(
 [pa.array([[{"before": 1}], [], None, [{"before": 3}]], type=arrow_schema.field(0).type)],
 schema=arrow_schema,
 )

 result = _to_requested_schema(
 requested_schema, file_schema, batch, downcast_ns_timestamp_to_us=False, include_field_ids=False
 )

 # Rebuilding the list from the projected element array is what carries the rename.
 # Casting instead would match the element fields by name and yield nulls throughout.
 assert result.column(0).to_pylist() == [[{"after": 1}], [], None, [{"after": 3}]]


def test_pyarrow_file_io_fs_by_scheme_cache() -> None:
 # It's better to set up multi-region minio servers for an integration test once `endpoint_url` argument
 # becomes available for `resolve_s3_region`
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Force GitHub README to respect dark mode\n(function() {\n var style = document.createElement('style');\n style.textContent = '\n .markdown-body {\n color-scheme: dark light;\n }\n .markdown-body pre { background: #161b22 !important; }\n .markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }\n .markdown-body table th, .markdown-body table td { border-color: #30363d !important; }\n .markdown-body img { background: #0d1117; }\n .markdown-body blockquote { border-left-color: #8b949e; }\n .markdown-body hr { border-color: #30363d; }\n ';\n document.head.appendChild(style);\n})();", "GitHub Dark Mode README Fix");
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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Fix null list of structs being read and written as an empty list#3834

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Fix null list of structs being read and written as an empty list
#3834
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69af7ae

Fix null list of structs being read and written as an empty list


slachiewicz Aug 23, 2026
1ee2f40

Keep the list rebuild for renamed fields, not for arrow#38809


slachiewicz Aug 23, 2026

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9 changes: 6 additions & 3 deletions
pyiceberg/io/pyarrow.py

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -2073,9 +2073,12 @@ def list(self, list_type: ListType, list_array: pa.Array | None, value_array: pa
 if isinstance(list_array, (pa.ListArray, pa.LargeListArray, pa.FixedSizeListArray)) and value_array is not None:
 list_initializer = pa.large_list if isinstance(list_array, pa.LargeListArray) else pa.list_
 if isinstance(value_array, pa.StructArray):
 # This can be removed once this has been fixed:
 # https://github.com/apache/arrow/issues/38809
 list_array = pa.LargeListArray.from_arrays(list_array.offsets, value_array)
 # Rebuilding is what applies the projection to the element struct. A plain
 # cast would not do: Iceberg renames by field-id, while cast matches the
 # element fields by name and would silently null out any renamed one. The
 # mask has to be carried over because the offsets buffer alone cannot
 # express a null list, only an empty one.
 list_array = pa.LargeListArray.from_arrays(list_array.offsets, value_array, mask=list_array.is_null())
 value_array = self._cast_if_needed(list_type.element_field, value_array)
 arrow_field = list_initializer(self._construct_field(list_type.element_field, value_array.type))
 return list_array.cast(arrow_field)
Expand Down

5 changes: 1 addition & 4 deletions
tests/integration/test_reads.py

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -994,10 +994,7 @@ def test_null_list_and_map(catalog: Catalog) -> None:
 arrow_table = table_test_empty_list_and_map.scan().to_arrow()
 assert arrow_table["col_list"].to_pylist() == [None, []]
 assert arrow_table["col_map"].to_pylist() == [None, []]
 # This should be:
 # assert arrow_table["col_list_with_struct"].to_pylist() == [None, [{'test': 1}]]
 # Once https://github.com/apache/arrow/issues/38809 has been fixed
 assert arrow_table["col_list_with_struct"].to_pylist() == [[], [{"test": 1}]]
 assert arrow_table["col_list_with_struct"].to_pylist() == [None, [{"test": 1}]]


@pytest.mark.integration
Expand Down

71 changes: 71 additions & 0 deletions
tests/io/test_pyarrow.py

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -3210,6 +3210,77 @@ def test__to_requested_schema_float_promotion(
 assert result.column(0).to_pylist() == [1.5, 2.25, 3.0, None]


def test__to_requested_schema_null_list_of_structs() -> None:
 """Test that a null list survives the write path when its element is a struct."""
 requested_schema = Schema(
 NestedField(
 1,
 "col_list_with_struct",
 ListType(11, StructType(NestedField(111, "test", IntegerType(), required=False)), element_required=False),
 required=False,
 ),
 NestedField(2, "col_list", ListType(21, IntegerType(), element_required=False), required=False),
 )
 file_schema = requested_schema

 arrow_schema = pa.schema(
 [
 pa.field("col_list_with_struct", pa.list_(pa.struct([pa.field("test", pa.int32())]))),
 pa.field("col_list", pa.list_(pa.int32())),
 ]
 )
 batch = pa.RecordBatch.from_arrays(
 [
 pa.array([[{"test": 1}], [], None], type=arrow_schema.field(0).type),
 pa.array([[1], [], None], type=arrow_schema.field(1).type),
 ],
 schema=arrow_schema,
 )

 result = _to_requested_schema(
 requested_schema, file_schema, batch, downcast_ns_timestamp_to_us=False, include_field_ids=False
 )

 # A null list and an empty list are different values, and only the struct-element
 # case ever collapsed the former into the latter.
 assert result.column(0).to_pylist() == [[{"test": 1}], [], None]
 assert result.column(1).to_pylist() == [[1], [], None]


def test__to_requested_schema_renamed_field_in_list_of_structs() -> None:
 """Test that a field renamed inside a list element keeps its values."""
 file_schema = Schema(
 NestedField(
 1,
 "col",
 ListType(11, StructType(NestedField(111, "before", IntegerType(), required=False)), element_required=False),
 required=False,
 ),
 )
 requested_schema = Schema(
 NestedField(
 1,
 "col",
 ListType(11, StructType(NestedField(111, "after", IntegerType(), required=False)), element_required=False),
 required=False,
 ),
 )

 arrow_schema = pa.schema([pa.field("col", pa.list_(pa.struct([pa.field("before", pa.int32())])))])
 batch = pa.RecordBatch.from_arrays(
 [pa.array([[{"before": 1}], [], None, [{"before": 3}]], type=arrow_schema.field(0).type)],
 schema=arrow_schema,
 )

 result = _to_requested_schema(
 requested_schema, file_schema, batch, downcast_ns_timestamp_to_us=False, include_field_ids=False
 )

 # Rebuilding the list from the projected element array is what carries the rename.
 # Casting instead would match the element fields by name and yield nulls throughout.
 assert result.column(0).to_pylist() == [[{"after": 1}], [], None, [{"after": 3}]]


def test_pyarrow_file_io_fs_by_scheme_cache() -> None:
 # It's better to set up multi-region minio servers for an integration test once `endpoint_url` argument
 # becomes available for `resolve_s3_region`
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Highlight search terms from Google/DuckDuckGo/Bing referrer\n(function() {\n var ref = document.referrer;\n var terms = [];\n \n if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {\n var url = new URL(ref);\n var q = url.searchParams.get('q') || url.searchParams.get('p');\n if (q) {\n terms = q.split(/\\s+/).filter(function(t) { return t.length > 2; });\n }\n }\n \n if (terms.length === 0) return;\n \n var style = document.createElement('style');\n style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';\n document.head.appendChild(style);\n \n function highlight(node) {\n if (node.nodeType === 3) { // text node\n var text = node.textContent;\n var found = false;\n terms.forEach(function(term) {\n var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\\]\\\\]/g, '\\\\') + ')', 'gi');\n if (regex.test(text)) {\n found = true;\n var frag = document.createDocumentFragment();\n var parts = text.split(regex);\n parts.forEach(function(part, i) {\n if (i % 2 === 0) {\n frag.appendChild(document.createTextNode(part));\n } else {\n var span = document.createElement('span');\n span.className = 'userscript-highlight';\n span.textContent = part;\n frag.appendChild(span);\n }\n });\n node.parentNode.replaceChild(frag, node);\n }\n });\n } else if (node.nodeType === 1 && node.childNodes) { // element\n var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];\n if (!skipTags.includes(node.tagName)) {\n Array.from(node.childNodes).forEach(highlight);\n }\n }\n }\n \n highlight(document.body);\n \n // Re-highlight on dynamic content\n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1 || node.nodeType === 3) highlight(node);\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Highlight Search Terms");
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
Fix null list of structs being read and written as an empty list#3834

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slachiewicz
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Fix null list of structs being read and written as an empty list
#3834
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69af7ae

Fix null list of structs being read and written as an empty list


slachiewicz Aug 23, 2026
1ee2f40

Keep the list rebuild for renamed fields, not for arrow#38809


slachiewicz Aug 23, 2026

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9 changes: 6 additions & 3 deletions
pyiceberg/io/pyarrow.py

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -2073,9 +2073,12 @@ def list(self, list_type: ListType, list_array: pa.Array | None, value_array: pa
 if isinstance(list_array, (pa.ListArray, pa.LargeListArray, pa.FixedSizeListArray)) and value_array is not None:
 list_initializer = pa.large_list if isinstance(list_array, pa.LargeListArray) else pa.list_
 if isinstance(value_array, pa.StructArray):
 # This can be removed once this has been fixed:
 # https://github.com/apache/arrow/issues/38809
 list_array = pa.LargeListArray.from_arrays(list_array.offsets, value_array)
 # Rebuilding is what applies the projection to the element struct. A plain
 # cast would not do: Iceberg renames by field-id, while cast matches the
 # element fields by name and would silently null out any renamed one. The
 # mask has to be carried over because the offsets buffer alone cannot
 # express a null list, only an empty one.
 list_array = pa.LargeListArray.from_arrays(list_array.offsets, value_array, mask=list_array.is_null())
 value_array = self._cast_if_needed(list_type.element_field, value_array)
 arrow_field = list_initializer(self._construct_field(list_type.element_field, value_array.type))
 return list_array.cast(arrow_field)
Expand Down

5 changes: 1 addition & 4 deletions
tests/integration/test_reads.py

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -994,10 +994,7 @@ def test_null_list_and_map(catalog: Catalog) -> None:
 arrow_table = table_test_empty_list_and_map.scan().to_arrow()
 assert arrow_table["col_list"].to_pylist() == [None, []]
 assert arrow_table["col_map"].to_pylist() == [None, []]
 # This should be:
 # assert arrow_table["col_list_with_struct"].to_pylist() == [None, [{'test': 1}]]
 # Once https://github.com/apache/arrow/issues/38809 has been fixed
 assert arrow_table["col_list_with_struct"].to_pylist() == [[], [{"test": 1}]]
 assert arrow_table["col_list_with_struct"].to_pylist() == [None, [{"test": 1}]]


@pytest.mark.integration
Expand Down

71 changes: 71 additions & 0 deletions
tests/io/test_pyarrow.py

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -3210,6 +3210,77 @@ def test__to_requested_schema_float_promotion(
 assert result.column(0).to_pylist() == [1.5, 2.25, 3.0, None]


def test__to_requested_schema_null_list_of_structs() -> None:
 """Test that a null list survives the write path when its element is a struct."""
 requested_schema = Schema(
 NestedField(
 1,
 "col_list_with_struct",
 ListType(11, StructType(NestedField(111, "test", IntegerType(), required=False)), element_required=False),
 required=False,
 ),
 NestedField(2, "col_list", ListType(21, IntegerType(), element_required=False), required=False),
 )
 file_schema = requested_schema

 arrow_schema = pa.schema(
 [
 pa.field("col_list_with_struct", pa.list_(pa.struct([pa.field("test", pa.int32())]))),
 pa.field("col_list", pa.list_(pa.int32())),
 ]
 )
 batch = pa.RecordBatch.from_arrays(
 [
 pa.array([[{"test": 1}], [], None], type=arrow_schema.field(0).type),
 pa.array([[1], [], None], type=arrow_schema.field(1).type),
 ],
 schema=arrow_schema,
 )

 result = _to_requested_schema(
 requested_schema, file_schema, batch, downcast_ns_timestamp_to_us=False, include_field_ids=False
 )

 # A null list and an empty list are different values, and only the struct-element
 # case ever collapsed the former into the latter.
 assert result.column(0).to_pylist() == [[{"test": 1}], [], None]
 assert result.column(1).to_pylist() == [[1], [], None]


def test__to_requested_schema_renamed_field_in_list_of_structs() -> None:
 """Test that a field renamed inside a list element keeps its values."""
 file_schema = Schema(
 NestedField(
 1,
 "col",
 ListType(11, StructType(NestedField(111, "before", IntegerType(), required=False)), element_required=False),
 required=False,
 ),
 )
 requested_schema = Schema(
 NestedField(
 1,
 "col",
 ListType(11, StructType(NestedField(111, "after", IntegerType(), required=False)), element_required=False),
 required=False,
 ),
 )

 arrow_schema = pa.schema([pa.field("col", pa.list_(pa.struct([pa.field("before", pa.int32())])))])
 batch = pa.RecordBatch.from_arrays(
 [pa.array([[{"before": 1}], [], None, [{"before": 3}]], type=arrow_schema.field(0).type)],
 schema=arrow_schema,
 )

 result = _to_requested_schema(
 requested_schema, file_schema, batch, downcast_ns_timestamp_to_us=False, include_field_ids=False
 )

 # Rebuilding the list from the projected element array is what carries the rename.
 # Casting instead would match the element fields by name and yield nulls throughout.
 assert result.column(0).to_pylist() == [[{"after": 1}], [], None, [{"after": 3}]]


def test_pyarrow_file_io_fs_by_scheme_cache() -> None:
 # It's better to set up multi-region minio servers for an integration test once `endpoint_url` argument
 # becomes available for `resolve_s3_region`
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Strip utm_, fbclid, gclid, etc. from all links on page\n(function() {\n var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',\n 'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',\n 'ref', 'ref_src', 'source', 'medium', 'campaign'];\n \n function cleanUrl(url) {\n try {\n var u = new URL(url, window.location.origin);\n var changed = false;\n trackingParams.forEach(function(p) {\n if (u.searchParams.has(p)) {\n u.searchParams.delete(p);\n changed = true;\n }\n });\n return changed ? u.toString() : url;\n } catch (e) {\n return url;\n }\n }\n \n function cleanLinks() {\n document.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n \n cleanLinks();\n \n var observer = new MutationObserver(function(mutations) {\n mutations.forEach(function(m) {\n m.addedNodes.forEach(function(node) {\n if (node.nodeType === 1) {\n if (node.tagName === 'A') cleanLinks();\n node.querySelectorAll('a[href]').forEach(function(a) {\n var clean = cleanUrl(a.href);\n if (clean !== a.href) a.href = clean;\n });\n }\n });\n });\n });\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "Remove Tracking Parameters from Links");
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

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Fix null list of structs being read and written as an empty list#3834

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Fix null list of structs being read and written as an empty list
#3834
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69af7ae

Fix null list of structs being read and written as an empty list


slachiewicz Aug 23, 2026
1ee2f40

Keep the list rebuild for renamed fields, not for arrow#38809


slachiewicz Aug 23, 2026

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9 changes: 6 additions & 3 deletions
pyiceberg/io/pyarrow.py

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -2073,9 +2073,12 @@ def list(self, list_type: ListType, list_array: pa.Array | None, value_array: pa
 if isinstance(list_array, (pa.ListArray, pa.LargeListArray, pa.FixedSizeListArray)) and value_array is not None:
 list_initializer = pa.large_list if isinstance(list_array, pa.LargeListArray) else pa.list_
 if isinstance(value_array, pa.StructArray):
 # This can be removed once this has been fixed:
 # https://github.com/apache/arrow/issues/38809
 list_array = pa.LargeListArray.from_arrays(list_array.offsets, value_array)
 # Rebuilding is what applies the projection to the element struct. A plain
 # cast would not do: Iceberg renames by field-id, while cast matches the
 # element fields by name and would silently null out any renamed one. The
 # mask has to be carried over because the offsets buffer alone cannot
 # express a null list, only an empty one.
 list_array = pa.LargeListArray.from_arrays(list_array.offsets, value_array, mask=list_array.is_null())
 value_array = self._cast_if_needed(list_type.element_field, value_array)
 arrow_field = list_initializer(self._construct_field(list_type.element_field, value_array.type))
 return list_array.cast(arrow_field)
Expand Down

5 changes: 1 addition & 4 deletions
tests/integration/test_reads.py

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -994,10 +994,7 @@ def test_null_list_and_map(catalog: Catalog) -> None:
 arrow_table = table_test_empty_list_and_map.scan().to_arrow()
 assert arrow_table["col_list"].to_pylist() == [None, []]
 assert arrow_table["col_map"].to_pylist() == [None, []]
 # This should be:
 # assert arrow_table["col_list_with_struct"].to_pylist() == [None, [{'test': 1}]]
 # Once https://github.com/apache/arrow/issues/38809 has been fixed
 assert arrow_table["col_list_with_struct"].to_pylist() == [[], [{"test": 1}]]
 assert arrow_table["col_list_with_struct"].to_pylist() == [None, [{"test": 1}]]


@pytest.mark.integration
Expand Down

71 changes: 71 additions & 0 deletions
tests/io/test_pyarrow.py

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -3210,6 +3210,77 @@ def test__to_requested_schema_float_promotion(
 assert result.column(0).to_pylist() == [1.5, 2.25, 3.0, None]


def test__to_requested_schema_null_list_of_structs() -> None:
 """Test that a null list survives the write path when its element is a struct."""
 requested_schema = Schema(
 NestedField(
 1,
 "col_list_with_struct",
 ListType(11, StructType(NestedField(111, "test", IntegerType(), required=False)), element_required=False),
 required=False,
 ),
 NestedField(2, "col_list", ListType(21, IntegerType(), element_required=False), required=False),
 )
 file_schema = requested_schema

 arrow_schema = pa.schema(
 [
 pa.field("col_list_with_struct", pa.list_(pa.struct([pa.field("test", pa.int32())]))),
 pa.field("col_list", pa.list_(pa.int32())),
 ]
 )
 batch = pa.RecordBatch.from_arrays(
 [
 pa.array([[{"test": 1}], [], None], type=arrow_schema.field(0).type),
 pa.array([[1], [], None], type=arrow_schema.field(1).type),
 ],
 schema=arrow_schema,
 )

 result = _to_requested_schema(
 requested_schema, file_schema, batch, downcast_ns_timestamp_to_us=False, include_field_ids=False
 )

 # A null list and an empty list are different values, and only the struct-element
 # case ever collapsed the former into the latter.
 assert result.column(0).to_pylist() == [[{"test": 1}], [], None]
 assert result.column(1).to_pylist() == [[1], [], None]


def test__to_requested_schema_renamed_field_in_list_of_structs() -> None:
 """Test that a field renamed inside a list element keeps its values."""
 file_schema = Schema(
 NestedField(
 1,
 "col",
 ListType(11, StructType(NestedField(111, "before", IntegerType(), required=False)), element_required=False),
 required=False,
 ),
 )
 requested_schema = Schema(
 NestedField(
 1,
 "col",
 ListType(11, StructType(NestedField(111, "after", IntegerType(), required=False)), element_required=False),
 required=False,
 ),
 )

 arrow_schema = pa.schema([pa.field("col", pa.list_(pa.struct([pa.field("before", pa.int32())])))])
 batch = pa.RecordBatch.from_arrays(
 [pa.array([[{"before": 1}], [], None, [{"before": 3}]], type=arrow_schema.field(0).type)],
 schema=arrow_schema,
 )

 result = _to_requested_schema(
 requested_schema, file_schema, batch, downcast_ns_timestamp_to_us=False, include_field_ids=False
 )

 # Rebuilding the list from the projected element array is what carries the rename.
 # Casting instead would match the element fields by name and yield nulls throughout.
 assert result.column(0).to_pylist() == [[{"after": 1}], [], None, [{"after": 3}]]


def test_pyarrow_file_io_fs_by_scheme_cache() -> None:
 # It's better to set up multi-region minio servers for an integration test once `endpoint_url` argument
 # becomes available for `resolve_s3_region`
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Auto-enable theater mode on YouTube\n(function() {\n function tryTheater() {\n var btn = document.querySelector('button[aria-label=\"Theater mode\"], ytd-player #player button[title=\"Theater mode\"]');\n if (btn && !btn.classList.contains('activated')) {\n btn.click();\n }\n }\n \n // Try immediately\n tryTheater();\n \n // Try after navigation (SPA)\n var lastUrl = location.href;\n setInterval(function() {\n if (location.href !== lastUrl) {\n lastUrl = location.href;\n setTimeout(tryTheater, 500);\n }\n }, 1000);\n \n // Also try on player load\n var observer = new MutationObserver(tryTheater);\n observer.observe(document.body, { childList: true, subtree: true });\n})();", "YouTube Theater Mode Default");
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
Fix null list of structs being read and written as an empty list#3834

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Fix null list of structs being read and written as an empty list
#3834
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69af7ae

Fix null list of structs being read and written as an empty list


slachiewicz Aug 23, 2026
1ee2f40

Keep the list rebuild for renamed fields, not for arrow#38809


slachiewicz Aug 23, 2026

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9 changes: 6 additions & 3 deletions
pyiceberg/io/pyarrow.py

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -2073,9 +2073,12 @@ def list(self, list_type: ListType, list_array: pa.Array | None, value_array: pa
 if isinstance(list_array, (pa.ListArray, pa.LargeListArray, pa.FixedSizeListArray)) and value_array is not None:
 list_initializer = pa.large_list if isinstance(list_array, pa.LargeListArray) else pa.list_
 if isinstance(value_array, pa.StructArray):
 # This can be removed once this has been fixed:
 # https://github.com/apache/arrow/issues/38809
 list_array = pa.LargeListArray.from_arrays(list_array.offsets, value_array)
 # Rebuilding is what applies the projection to the element struct. A plain
 # cast would not do: Iceberg renames by field-id, while cast matches the
 # element fields by name and would silently null out any renamed one. The
 # mask has to be carried over because the offsets buffer alone cannot
 # express a null list, only an empty one.
 list_array = pa.LargeListArray.from_arrays(list_array.offsets, value_array, mask=list_array.is_null())
 value_array = self._cast_if_needed(list_type.element_field, value_array)
 arrow_field = list_initializer(self._construct_field(list_type.element_field, value_array.type))
 return list_array.cast(arrow_field)
Expand Down

5 changes: 1 addition & 4 deletions
tests/integration/test_reads.py

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -994,10 +994,7 @@ def test_null_list_and_map(catalog: Catalog) -> None:
 arrow_table = table_test_empty_list_and_map.scan().to_arrow()
 assert arrow_table["col_list"].to_pylist() == [None, []]
 assert arrow_table["col_map"].to_pylist() == [None, []]
 # This should be:
 # assert arrow_table["col_list_with_struct"].to_pylist() == [None, [{'test': 1}]]
 # Once https://github.com/apache/arrow/issues/38809 has been fixed
 assert arrow_table["col_list_with_struct"].to_pylist() == [[], [{"test": 1}]]
 assert arrow_table["col_list_with_struct"].to_pylist() == [None, [{"test": 1}]]


@pytest.mark.integration
Expand Down

71 changes: 71 additions & 0 deletions
tests/io/test_pyarrow.py

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -3210,6 +3210,77 @@ def test__to_requested_schema_float_promotion(
 assert result.column(0).to_pylist() == [1.5, 2.25, 3.0, None]


def test__to_requested_schema_null_list_of_structs() -> None:
 """Test that a null list survives the write path when its element is a struct."""
 requested_schema = Schema(
 NestedField(
 1,
 "col_list_with_struct",
 ListType(11, StructType(NestedField(111, "test", IntegerType(), required=False)), element_required=False),
 required=False,
 ),
 NestedField(2, "col_list", ListType(21, IntegerType(), element_required=False), required=False),
 )
 file_schema = requested_schema

 arrow_schema = pa.schema(
 [
 pa.field("col_list_with_struct", pa.list_(pa.struct([pa.field("test", pa.int32())]))),
 pa.field("col_list", pa.list_(pa.int32())),
 ]
 )
 batch = pa.RecordBatch.from_arrays(
 [
 pa.array([[{"test": 1}], [], None], type=arrow_schema.field(0).type),
 pa.array([[1], [], None], type=arrow_schema.field(1).type),
 ],
 schema=arrow_schema,
 )

 result = _to_requested_schema(
 requested_schema, file_schema, batch, downcast_ns_timestamp_to_us=False, include_field_ids=False
 )

 # A null list and an empty list are different values, and only the struct-element
 # case ever collapsed the former into the latter.
 assert result.column(0).to_pylist() == [[{"test": 1}], [], None]
 assert result.column(1).to_pylist() == [[1], [], None]


def test__to_requested_schema_renamed_field_in_list_of_structs() -> None:
 """Test that a field renamed inside a list element keeps its values."""
 file_schema = Schema(
 NestedField(
 1,
 "col",
 ListType(11, StructType(NestedField(111, "before", IntegerType(), required=False)), element_required=False),
 required=False,
 ),
 )
 requested_schema = Schema(
 NestedField(
 1,
 "col",
 ListType(11, StructType(NestedField(111, "after", IntegerType(), required=False)), element_required=False),
 required=False,
 ),
 )

 arrow_schema = pa.schema([pa.field("col", pa.list_(pa.struct([pa.field("before", pa.int32())])))])
 batch = pa.RecordBatch.from_arrays(
 [pa.array([[{"before": 1}], [], None, [{"before": 3}]], type=arrow_schema.field(0).type)],
 schema=arrow_schema,
 )

 result = _to_requested_schema(
 requested_schema, file_schema, batch, downcast_ns_timestamp_to_us=False, include_field_ids=False
 )

 # Rebuilding the list from the projected element array is what carries the rename.
 # Casting instead would match the element fields by name and yield nulls throughout.
 assert result.column(0).to_pylist() == [[{"after": 1}], [], None, [{"after": 3}]]


def test_pyarrow_file_io_fs_by_scheme_cache() -> None:
 # It's better to set up multi-region minio servers for an integration test once `endpoint_url` argument
 # becomes available for `resolve_s3_region`
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Remove or un-stick sticky/fixed headers that block content\n(function() {\n function unstick() {\n document.querySelectorAll('header, nav, [role=\"banner\"], .header, .navbar, .sticky, .fixed-top, [style*=\"position: fixed\"], [style*=\"position:sticky\"]').forEach(function(el) {\n if (el.style.position === 'fixed' || el.style.position === 'sticky' || \n getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {\n el.style.position = 'static';\n el.style.top = 'auto';\n el.style.zIndex = 'auto';\n }\n });\n }\n \n unstick();\n \n var observer = new MutationObserver(unstick);\n observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });\n})();", "Kill Sticky Headers");
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
Fix null list of structs being read and written as an empty list#3834

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slachiewicz
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Fix null list of structs being read and written as an empty list
#3834
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69af7ae

Fix null list of structs being read and written as an empty list


slachiewicz Aug 23, 2026
1ee2f40

Keep the list rebuild for renamed fields, not for arrow#38809


slachiewicz Aug 23, 2026

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9 changes: 6 additions & 3 deletions
pyiceberg/io/pyarrow.py

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -2073,9 +2073,12 @@ def list(self, list_type: ListType, list_array: pa.Array | None, value_array: pa
 if isinstance(list_array, (pa.ListArray, pa.LargeListArray, pa.FixedSizeListArray)) and value_array is not None:
 list_initializer = pa.large_list if isinstance(list_array, pa.LargeListArray) else pa.list_
 if isinstance(value_array, pa.StructArray):
 # This can be removed once this has been fixed:
 # https://github.com/apache/arrow/issues/38809
 list_array = pa.LargeListArray.from_arrays(list_array.offsets, value_array)
 # Rebuilding is what applies the projection to the element struct. A plain
 # cast would not do: Iceberg renames by field-id, while cast matches the
 # element fields by name and would silently null out any renamed one. The
 # mask has to be carried over because the offsets buffer alone cannot
 # express a null list, only an empty one.
 list_array = pa.LargeListArray.from_arrays(list_array.offsets, value_array, mask=list_array.is_null())
 value_array = self._cast_if_needed(list_type.element_field, value_array)
 arrow_field = list_initializer(self._construct_field(list_type.element_field, value_array.type))
 return list_array.cast(arrow_field)
Expand Down

5 changes: 1 addition & 4 deletions
tests/integration/test_reads.py

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -994,10 +994,7 @@ def test_null_list_and_map(catalog: Catalog) -> None:
 arrow_table = table_test_empty_list_and_map.scan().to_arrow()
 assert arrow_table["col_list"].to_pylist() == [None, []]
 assert arrow_table["col_map"].to_pylist() == [None, []]
 # This should be:
 # assert arrow_table["col_list_with_struct"].to_pylist() == [None, [{'test': 1}]]
 # Once https://github.com/apache/arrow/issues/38809 has been fixed
 assert arrow_table["col_list_with_struct"].to_pylist() == [[], [{"test": 1}]]
 assert arrow_table["col_list_with_struct"].to_pylist() == [None, [{"test": 1}]]


@pytest.mark.integration
Expand Down

71 changes: 71 additions & 0 deletions
tests/io/test_pyarrow.py

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -3210,6 +3210,77 @@ def test__to_requested_schema_float_promotion(
 assert result.column(0).to_pylist() == [1.5, 2.25, 3.0, None]


def test__to_requested_schema_null_list_of_structs() -> None:
 """Test that a null list survives the write path when its element is a struct."""
 requested_schema = Schema(
 NestedField(
 1,
 "col_list_with_struct",
 ListType(11, StructType(NestedField(111, "test", IntegerType(), required=False)), element_required=False),
 required=False,
 ),
 NestedField(2, "col_list", ListType(21, IntegerType(), element_required=False), required=False),
 )
 file_schema = requested_schema

 arrow_schema = pa.schema(
 [
 pa.field("col_list_with_struct", pa.list_(pa.struct([pa.field("test", pa.int32())]))),
 pa.field("col_list", pa.list_(pa.int32())),
 ]
 )
 batch = pa.RecordBatch.from_arrays(
 [
 pa.array([[{"test": 1}], [], None], type=arrow_schema.field(0).type),
 pa.array([[1], [], None], type=arrow_schema.field(1).type),
 ],
 schema=arrow_schema,
 )

 result = _to_requested_schema(
 requested_schema, file_schema, batch, downcast_ns_timestamp_to_us=False, include_field_ids=False
 )

 # A null list and an empty list are different values, and only the struct-element
 # case ever collapsed the former into the latter.
 assert result.column(0).to_pylist() == [[{"test": 1}], [], None]
 assert result.column(1).to_pylist() == [[1], [], None]


def test__to_requested_schema_renamed_field_in_list_of_structs() -> None:
 """Test that a field renamed inside a list element keeps its values."""
 file_schema = Schema(
 NestedField(
 1,
 "col",
 ListType(11, StructType(NestedField(111, "before", IntegerType(), required=False)), element_required=False),
 required=False,
 ),
 )
 requested_schema = Schema(
 NestedField(
 1,
 "col",
 ListType(11, StructType(NestedField(111, "after", IntegerType(), required=False)), element_required=False),
 required=False,
 ),
 )

 arrow_schema = pa.schema([pa.field("col", pa.list_(pa.struct([pa.field("before", pa.int32())])))])
 batch = pa.RecordBatch.from_arrays(
 [pa.array([[{"before": 1}], [], None, [{"before": 3}]], type=arrow_schema.field(0).type)],
 schema=arrow_schema,
 )

 result = _to_requested_schema(
 requested_schema, file_schema, batch, downcast_ns_timestamp_to_us=False, include_field_ids=False
 )

 # Rebuilding the list from the projected element array is what carries the rename.
 # Casting instead would match the element fields by name and yield nulls throughout.
 assert result.column(0).to_pylist() == [[{"after": 1}], [], None, [{"after": 3}]]


def test_pyarrow_file_io_fs_by_scheme_cache() -> None:
 # It's better to set up multi-region minio servers for an integration test once `endpoint_url` argument
 # becomes available for `resolve_s3_region`
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
injectUserscript("// Universal Dark Mode - works on any site\n(function() {\n var enabled = true;\n \n function applyDarkMode() {\n if (!enabled) return;\n \n // Create style element if it doesn't exist\n var style = document.getElementById('universal-dark-mode-style');\n if (!style) {\n style = document.createElement('style');\n style.id = 'universal-dark-mode-style';\n document.head.appendChild(style);\n }\n \n // Dark mode CSS - inverts colors but preserves images/video\n style.textContent = '\n /* Invert everything except media */\n html {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #1a1a2e !important;\n }\n \n /* Restore images, videos, iframes, canvas */\n img, video, iframe, canvas, svg, picture, [style*=\"background-image\"] {\n filter: invert(1) hue-rotate(180deg) !important;\n }\n \n /* Preserve specific elements that should not be inverted */\n .no-dark-mode, .no-dark-mode *,\n [data-theme=\"light\"], [data-theme=\"light\"],\n .ace_editor, .ace_editor *,\n .CodeMirror, .CodeMirror *,\n .monaco-editor, .monaco-editor *,\n .markdown-body pre, .markdown-body pre *,\n .highlight, .highlight *,\n pre code, pre code * {\n filter: none !important;\n }\n \n /* Fix common UI elements */\n .modal, .popup, .dropdown-menu, .tooltip, .popover {\n filter: invert(1) hue-rotate(180deg) !important;\n background: #2d2d44 !important;\n border-color: #444 !important;\n }\n \n /* Scrollbars */\n ::-webkit-scrollbar { background: #1a1a2e !important; }\n ::-webkit-scrollbar-thumb { background: #444 !important; }\n ::-webkit-scrollbar-thumb:hover { background: #555 !important; }\n \n /* Selection */\n ::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }\n ';\n }\n \n function removeDarkMode() {\n var style = document.getElementById('universal-dark-mode-style');\n if (style) style.remove();\n }\n \n // Toggle with Alt+Shift+D\n document.addEventListener('keydown', function(e) {\n if (e.altKey && e.shiftKey && e.key === 'D') {\n e.preventDefault();\n enabled = !enabled;\n if (enabled) {\n applyDarkMode();\n console.log('[Universal Dark Mode] Enabled');\n } else {\n removeDarkMode();\n console.log('[Universal Dark Mode] Disabled');\n }\n }\n });\n \n // Apply on load\n applyDarkMode();\n \n // Re-apply on dynamic content\n var observer = new MutationObserver(function(mutations) {\n if (enabled && !document.getElementById('universal-dark-mode-style')) {\n applyDarkMode();\n }\n });\n observer.observe(document.head, { childList: true });\n \n console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');\n})();", "Universal Dark Mode");
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

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Fix null list of structs being read and written as an empty list#3834

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Fix null list of structs being read and written as an empty list
#3834
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69af7ae

Fix null list of structs being read and written as an empty list


slachiewicz Aug 23, 2026
1ee2f40

Keep the list rebuild for renamed fields, not for arrow#38809


slachiewicz Aug 23, 2026

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9 changes: 6 additions & 3 deletions
pyiceberg/io/pyarrow.py

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Original file line numberDiff line numberDiff line change
Expand Up@@ -2073,9 +2073,12 @@ def list(self, list_type: ListType, list_array: pa.Array | None, value_array: pa
 if isinstance(list_array, (pa.ListArray, pa.LargeListArray, pa.FixedSizeListArray)) and value_array is not None:
 list_initializer = pa.large_list if isinstance(list_array, pa.LargeListArray) else pa.list_
 if isinstance(value_array, pa.StructArray):
 # This can be removed once this has been fixed:
 # https://github.com/apache/arrow/issues/38809
 list_array = pa.LargeListArray.from_arrays(list_array.offsets, value_array)
 # Rebuilding is what applies the projection to the element struct. A plain
 # cast would not do: Iceberg renames by field-id, while cast matches the
 # element fields by name and would silently null out any renamed one. The
 # mask has to be carried over because the offsets buffer alone cannot
 # express a null list, only an empty one.
 list_array = pa.LargeListArray.from_arrays(list_array.offsets, value_array, mask=list_array.is_null())
 value_array = self._cast_if_needed(list_type.element_field, value_array)
 arrow_field = list_initializer(self._construct_field(list_type.element_field, value_array.type))
 return list_array.cast(arrow_field)
Expand Down

5 changes: 1 addition & 4 deletions
tests/integration/test_reads.py

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Original file line numberDiff line numberDiff line change
Expand Up@@ -994,10 +994,7 @@ def test_null_list_and_map(catalog: Catalog) -> None:
 arrow_table = table_test_empty_list_and_map.scan().to_arrow()
 assert arrow_table["col_list"].to_pylist() == [None, []]
 assert arrow_table["col_map"].to_pylist() == [None, []]
 # This should be:
 # assert arrow_table["col_list_with_struct"].to_pylist() == [None, [{'test': 1}]]
 # Once https://github.com/apache/arrow/issues/38809 has been fixed
 assert arrow_table["col_list_with_struct"].to_pylist() == [[], [{"test": 1}]]
 assert arrow_table["col_list_with_struct"].to_pylist() == [None, [{"test": 1}]]


@pytest.mark.integration
Expand Down

71 changes: 71 additions & 0 deletions
tests/io/test_pyarrow.py

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Original file line numberDiff line numberDiff line change
Expand Up@@ -3210,6 +3210,77 @@ def test__to_requested_schema_float_promotion(
 assert result.column(0).to_pylist() == [1.5, 2.25, 3.0, None]


def test__to_requested_schema_null_list_of_structs() -> None:
 """Test that a null list survives the write path when its element is a struct."""
 requested_schema = Schema(
 NestedField(
 1,
 "col_list_with_struct",
 ListType(11, StructType(NestedField(111, "test", IntegerType(), required=False)), element_required=False),
 required=False,
 ),
 NestedField(2, "col_list", ListType(21, IntegerType(), element_required=False), required=False),
 )
 file_schema = requested_schema

 arrow_schema = pa.schema(
 [
 pa.field("col_list_with_struct", pa.list_(pa.struct([pa.field("test", pa.int32())]))),
 pa.field("col_list", pa.list_(pa.int32())),
 ]
 )
 batch = pa.RecordBatch.from_arrays(
 [
 pa.array([[{"test": 1}], [], None], type=arrow_schema.field(0).type),
 pa.array([[1], [], None], type=arrow_schema.field(1).type),
 ],
 schema=arrow_schema,
 )

 result = _to_requested_schema(
 requested_schema, file_schema, batch, downcast_ns_timestamp_to_us=False, include_field_ids=False
 )

 # A null list and an empty list are different values, and only the struct-element
 # case ever collapsed the former into the latter.
 assert result.column(0).to_pylist() == [[{"test": 1}], [], None]
 assert result.column(1).to_pylist() == [[1], [], None]


def test__to_requested_schema_renamed_field_in_list_of_structs() -> None:
 """Test that a field renamed inside a list element keeps its values."""
 file_schema = Schema(
 NestedField(
 1,
 "col",
 ListType(11, StructType(NestedField(111, "before", IntegerType(), required=False)), element_required=False),
 required=False,
 ),
 )
 requested_schema = Schema(
 NestedField(
 1,
 "col",
 ListType(11, StructType(NestedField(111, "after", IntegerType(), required=False)), element_required=False),
 required=False,
 ),
 )

 arrow_schema = pa.schema([pa.field("col", pa.list_(pa.struct([pa.field("before", pa.int32())])))])
 batch = pa.RecordBatch.from_arrays(
 [pa.array([[{"before": 1}], [], None, [{"before": 3}]], type=arrow_schema.field(0).type)],
 schema=arrow_schema,
 )

 result = _to_requested_schema(
 requested_schema, file_schema, batch, downcast_ns_timestamp_to_us=False, include_field_ids=False
 )

 # Rebuilding the list from the projected element array is what carries the rename.
 # Casting instead would match the element fields by name and yield nulls throughout.
 assert result.column(0).to_pylist() == [[{"after": 1}], [], None, [{"after": 3}]]


def test_pyarrow_file_io_fs_by_scheme_cache() -> None:
 # It's better to set up multi-region minio servers for an integration test once `endpoint_url` argument
 # becomes available for `resolve_s3_region`
Expand Down