>>> df = spark.createDataFrame([(2, "Alice"), (5, "Bob")], ["age", "name"])
>>> df._ipython_key_completions_()
['age', 'name']

>>> df = spark.createDataFrame([(2, "Alice"), (5, "Bob")], ["age 1", "name?1"])
>>> df._ipython_key_completions_()
['age 1', 'name?1']
