Major Description
Using Spark in a Jupyter Notebook 5.0 with an IPython 6.0 kernel and Python 3, when I press Tab to autocomplete the function names on a DataFrame or RDD, Spark executes the job graph constructed thus far. This only appears to happen for certain autocompletions, namely completions that resolve to functions having the @ignore_unicode_prefix decorator applied to them, and only in Python 3 (never in Python 2).
https://github.com/apache/spark/blob/master/python/pyspark/rdd.py#L146
Indeed, this function does have a special case for Python 3 in which it rewrites function docstrings. Why IPython autocompletion has a bad interaction with this logic is unknown (to me at least) at the moment.
I reproduced this bug on Spark 2.0.2. The code in the decorator hasn't changed in 2.1.x, so the bug likely impacts that version as well.