I would think the USING FILE would work.

As long as you follow the class_name requirements.

The implementing class should extend one of the base classes as follows:

• Should extend UDF or UDAF in org.apache.hadoop.hive.ql.exec package.
• Should extend AbstractGenericUDAFResolver, GenericUDF, or GenericUDTF in org.apache.hadoop.hive.ql.udf.generic package.
• Should extend UserDefinedAggregateFunction in org.apache.spark.sql.expressions package.

Also the docs literally state python is possible:

In addition to the SQL interface, Spark allows you to create custom user defined scalar and aggregate functions using Scala, Python, and Java APIs. See User-defined scalar functions (UDFs) and User-defined aggregate functions (UDAFs) for more information.

So it should be possible, maybe your python class does not meet the requirements?