df.explain("mode") should work in PySpark side as well for consistency

scala> spark.range(10).explain("cost")
== Optimized Logical Plan ==
Range (0, 10, step=1, splits=Some(12)), Statistics(sizeInBytes=80.0 B)

== Physical Plan ==
*(1) Range (0, 10, step=1, splits=12)

>>> spark.range(10).explain("cost")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/.../spark/python/pyspark/sql/dataframe.py", line 333, in explain
    raise TypeError(err_msg)
TypeError: extended (optional) should be provided as bool, got <class 'str'>