Code contributions to Vumi should:
For classes, __init__ should be documented in the class docstring.
Function docstrings should look like:
def format_exception(etype, value, tb, limit=None):
"""Format the exception with a traceback.
:type etype: exception class
:param etype: exception type
:param value: exception value
:param tb: traceback object
:param limit: maximum number of stack frames to show
:type limit: integer or None
:rtype: list of strings
"""