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fix(python): on frame-init from generator, initial chunk_size cannot be smaller than infer_schema_length #6541

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Jan 29, 2023
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fix(python): on frame-init from generator, initial chunk_size cannot be smaller than infer_schema_length #6541

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10 changes: 7 additions & 3 deletions py-polars/polars/internals/construction.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1164,17 +1164,21 @@ def to_frame_chunk(
adaptive_chunk_size = None

df: pli.DataFrame = None # type: ignore[assignment]
chunk_size = max(
(infer_schema_length or 0),
(adaptive_chunk_size or 1000),
)
while True:
values = list(islice(data, adaptive_chunk_size or 1000))
values = list(islice(data, chunk_size))
if not values:
break
frame_chunk = to_frame_chunk(values, original_schema)
if df is None:
df = frame_chunk
if not original_schema:
original_schema = list(df.schema.items())
if not adaptive_chunk_size:
adaptive_chunk_size = n_chunk_elems // len(df.columns)
if chunk_size != adaptive_chunk_size:
chunk_size = adaptive_chunk_size = n_chunk_elems // len(df.columns)
else:
df.vstack(frame_chunk, in_place=True)
n_chunks += 1
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4 changes: 2 additions & 2 deletions py-polars/polars/internals/expr/expr.py
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Expand Up @@ -99,8 +99,8 @@ def expr_to_lit_or_expr(
expr
Any argument.
str_to_lit
If True string argument `"foo"` will be converted to `lit("foo")`,
If False it will be converted to `col("foo")`
If True string argument `"foo"` will be converted to `lit("foo")`.
If False it will be converted to `col("foo")`.

Returns
-------
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8 changes: 8 additions & 0 deletions py-polars/tests/unit/test_df.py
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Expand Up @@ -1265,6 +1265,14 @@ def __iter__(self) -> Iterator[Any]:
assert expected_data == d.row_tuples()
assert expected_schema == list(zip(d.columns(), d.dtypes()))

# ref: issue #6489 (initial chunk_size cannot be smaller than 'infer_schema_length')
df = pl.DataFrame(
data=iter(([{"col": None}] * 1000) + [{"col": ["a", "b", "c"]}]),
infer_schema_length=1001,
)
assert df.schema == {"col": pl.List(pl.Utf8)}
assert df[-2:]["col"].to_list() == [None, ["a", "b", "c"]]

# empty iterator
assert_frame_equal(
pl.DataFrame(data=gen(0), schema=["a", "b", "c", "d"]),
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