[arrow] branch main updated: GH-37050: [Python][Interchange protocol] Add a workaround for empty dataframes (#38037)

[jorisvandenbossche]

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The following commit(s) were added to refs/heads/main by this push:
     new 9afa848e64 GH-37050: [Python][Interchange protocol] Add a workaround 
for empty dataframes (#38037)
9afa848e64 is described below

commit 9afa848e640fbd7539e7a188657fcf2ae6e45245
Author: Alenka Frim <alen...@users.noreply.github.com>
AuthorDate: Tue Oct 10 13:18:35 2023 +0200

    GH-37050: [Python][Interchange protocol] Add a workaround for empty 
dataframes (#38037)
    
    ### Rationale for this change
    
    The implementation of the DataFrame Interchange Protocol does not currently 
support consumption of dataframes with 0 number of chunks (empty dataframes).
    
    ### What changes are included in this PR?
    
    Add a workaround to not error in this case.
    
    ### Are these changes tested?
    
    Yes, added `test_empty_dataframe` in 
`python/pyarrow/tests/interchange/test_conversion.py`.
    
    ### Are there any user-facing changes?
    No.
    * Closes: #37050
    
    Authored-by: AlenkaF <frim.ale...@gmail.com>
    Signed-off-by: Joris Van den Bossche <jorisvandenboss...@gmail.com>
---
 python/pyarrow/interchange/from_dataframe.py        | 4 ++++
 python/pyarrow/tests/interchange/test_conversion.py | 7 +++++++
 2 files changed, 11 insertions(+)

diff --git a/python/pyarrow/interchange/from_dataframe.py 
b/python/pyarrow/interchange/from_dataframe.py
index e97e91e44f..3767b18f2a 100644
--- a/python/pyarrow/interchange/from_dataframe.py
+++ b/python/pyarrow/interchange/from_dataframe.py
@@ -136,6 +136,10 @@ def _from_dataframe(df: DataFrameObject, allow_copy=True):
         batch = protocol_df_chunk_to_pyarrow(chunk, allow_copy)
         batches.append(batch)
 
+    if not batches:
+        batch = protocol_df_chunk_to_pyarrow(df)
+        batches.append(batch)
+
     return pa.Table.from_batches(batches)
 
 
diff --git a/python/pyarrow/tests/interchange/test_conversion.py 
b/python/pyarrow/tests/interchange/test_conversion.py
index 225210d8c7..b1e0fa0d1c 100644
--- a/python/pyarrow/tests/interchange/test_conversion.py
+++ b/python/pyarrow/tests/interchange/test_conversion.py
@@ -513,3 +513,10 @@ def test_allow_copy_false_bool_categorical():
     df = df.astype("category")
     with pytest.raises(RuntimeError):
         pi.from_dataframe(df, allow_copy=False)
+
+
+def test_empty_dataframe():
+    schema = pa.schema([('col1', pa.int8())])
+    df = pa.table([[]], schema=schema)
+    dfi = df.__dataframe__()
+    assert pi.from_dataframe(dfi) == df