code: def _create_function(name, doc=""):
      
      def _(col):
          sc = SparkContext._active_spark_context
          jc = getattr(sc._jvm.functions, name)(col._jc if isinstance(col, Column) else col)
          return Column(jc)
      _.__name__ = name
      _.__doc__ = doc
      return _
docs: Create a PySpark function by its name