I think we still need this in order to respect the user's PYTHONSTARTUP setting rather than just overwriting it; OLD_PYTHONSTARTUP is loaded inside of the `shell.py` script: https://github.com/pwendell/incubator-spark/blob/ipython-simplify/python/pyspark/shell.py?pr=%2Fapache%2Fincubator-spark%2Fpull%2F353#L52.