fix: show results in the nine silent top-level examples

Nine examples (`export.py`, `import.py`, `python-udaf.py`,
`python-udf.py`, `query-pyarrow-data.py`, `sql-to-pandas.py`,
`sql-using-python-udaf.py`, `sql-using-python-udf.py`, `substrait.py`)
ended in bare asserts and printed nothing, so a reader running them
sees no output and cannot tell a working script from a silent one
(#1728). Each now shows its final result with `df.show()` or a
terminal `print`, keeping the asserts.

Author: ump45nose

examples/export.py

@@ -50,3 +50,6 @@
 # export to Python dictionary of columns
 pydict = df.to_pydict()
 assert pydict == {"a": [1, 2, 3], "b": [4, 5, 6]}
+
+print(f"Exported as list of rows: {pylist}")
+print(f"Exported as dict of columns: {pydict}")

examples/import.py

@@ -55,3 +55,6 @@
 arrow_table = pa.Table.from_pydict({"a": [1, 2, 3], "b": [4, 5, 6]})
 df = ctx.from_arrow(arrow_table)
 assert type(df) is datafusion.DataFrame
+
+# Display the last converted DataFrame
+df.show()

examples/python-udaf.py

@@ -67,3 +67,5 @@ def evaluate(self) -> pa.Scalar:
 result = df.collect()[0]
 
 assert result.column(0) == pa.array([6.0])
+
+print(f"Sum of column 'a': {result.column(0)[0].as_py()}")

examples/python-udf.py

@@ -38,6 +38,8 @@ def is_null(array: pa.Array) -> pa.Array:
 
 df = df.select(is_null_arr(f.col("a")))
 
+df.show()
+
 result = df.collect()[0]
 
 assert result.column(0) == pa.array([False] * 3)

examples/query-pyarrow-data.py

@@ -35,6 +35,8 @@
     col("a") - col("b"),
 )
 
+df.show()
+
 # execute and collect the first (and only) batch
 result = df.collect()[0]
 

examples/sql-to-pandas.py

@@ -40,3 +40,5 @@
     kind="bar", title="Trip Count by Number of Passengers"
 ).get_figure()
 fig.savefig("chart.png")
+
+print("Saved chart to chart.png")

examples/sql-using-python-udaf.py

@@ -75,6 +75,7 @@ def evaluate(self) -> pa.Scalar:
 result_df = ctx.sql(
     "select a, my_accumulator(b) as b_aggregated from t group by a order by a"
 )
+result_df.show()
 # Dataframe:
 # +---+--------------+
 # | a | b_aggregated |

examples/sql-using-python-udf.py

@@ -53,6 +53,7 @@ def is_null(array: pa.Array) -> pa.Array:
 
 # Query the DataFrame using SQL
 result_df = ctx.sql("select a, is_null(b) as b_is_null from t")
+result_df.show()
 # Dataframe:
 # +---+-----------+
 # | a | b_is_null |

examples/substrait.py

@@ -47,3 +47,5 @@
 # Back to Substrait Plan just for demonstration purposes
 # type(substrait_plan) -> <class 'datafusion.substrait.plan'>
 substrait_plan = ss.Producer.to_substrait_plan(df_logical_plan, ctx)
+
+print(f"Substrait plan round-trip complete: {len(substrait_bytes)} encoded bytes")