[Mailman-Developers] Whoosh Error during installation of hyperkitty

[Nikhil Rayaprolu]

Hello I am new to the Mailman community and on my try to contribute for
Mailman,I started installing all packages . For Hyperkitty I followed
https://hyperkitty.readthedocs.io/en/latest/development.html . Everything
went fine without any errors but on accessing the hyperkitty on my browser
, it shows me an error stating "A server error occurred.  Please contact
the administrator."
and on the terminal the last 3 lines shows

File
"/home/nikhil/dev/mailman/venv2/local/lib/python2.7/site-packages/django_haystack-2.5.1-py2.7.egg/haystack/backends/whoosh_backend.py",
line 30, in <module>
    raise MissingDependency("The 'whoosh' backend requires the installation
of 'Whoosh'. Please refer to the documentation.")
MissingDependency: The 'whoosh' backend requires the installation of
'Whoosh'. Please refer to the documentation.

Can any one help me with figuring out the cause for this error