Move expr.py to doctestable examples

Author: ntjohnson1

python/datafusion/expr.py

@@ -342,7 +342,7 @@ def sort_list_to_raw_sort_list(
     return raw_sort_list
 
 
-class Expr:
+class Expr:  # noqa: PLW1641
     """Expression object.
 
     Expressions are one of the core concepts in DataFusion. See
@@ -1367,16 +1367,18 @@ def is_unbounded(self) -> bool:
 class CaseBuilder:
     """Builder class for constructing case statements.
 
-    An example usage would be as follows::
-
-        import datafusion.functions as f
-        from datafusion import lit, col
-        df.select(
-            f.case(col("column_a"))
-            .when(lit(1), lit("One"))
-            .when(lit(2), lit("Two"))
-            .otherwise(lit("Unknown"))
-        )
+    Examples:
+        >>> ctx = dfn.SessionContext()
+        >>> df = ctx.from_pydict({"a": [1, 2, 3]})
+        >>> result = df.select(
+        ...     dfn.functions.case(dfn.col("a"))
+        ...     .when(dfn.lit(1), dfn.lit("One"))
+        ...     .when(dfn.lit(2), dfn.lit("Two"))
+        ...     .otherwise(dfn.lit("Other"))
+        ...     .alias("label")
+        ... )
+        >>> result.to_pydict()
+        {'label': ['One', 'Two', 'Other']}
     """
 
     def __init__(self, case_builder: expr_internal.CaseBuilder) -> None: