Many times, when I'm setting up a cluster, I have to use an operating system (as RedHat or CentOS 6.5) which has an old version of Python (Python 2.6). For example, when using a Hadoop distribution that only supports those operating systems (as Hortonworks' HDP or Cloudera).
And that also makes installing additional advanced Python packages difficult (such as Numpy, IPython, etc).
Then I tend to use Anaconda Python, an open source version of Python with many of those packages pre-built and pre-installed.
But installing Anaconda in each node of the cluster might be tedious.