Comment by Kate Stone (JIRA)

The module "six" is part of the Python 2.7 package installed by default on OS X which is a required dependency of LLDB and therefore the Swift REPL. I don't suppose you have a custom version of Python installed?

You can debug the attempt to find modules by starting the Python interpreter in verbose mode:

$ python -v
<lots of output here>
>>> import six

1. /System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/six.pyc matches /System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/six.py
   <more output here>

Comment by Kate Stone (JIRA)

Works correctly on a typical OS X installation which includes the six module as part of Python 2.7.

As a sort of addendum: This problem occurs when an Apple-provided lldb is launched with a custom python interpreter (e.g. one from homebrew) in the path ahead of the Apple provided system python. Unfortunately, lldb doesn't hard-code the path to the python it wants to use but instead takes the first one it happens to stumble upon in the path (which may be missing the required modules).

Also reported as rdar://25314779