httpretty listed twice in requirements.txt

[shoemakerlevy9]

When trying to install python dependencies using the command

sudo pip install -r requirements.txt

I get the following error

Double requirement given: httpretty (from -r requirements.txt (line 6)) (already in httpretty (from -r requirements.txt (line 2)), name='httpretty')

Upon Inspecting the requirements.txt file I see that it is correct, httpretty is listed twice

construct==2.8.12
httpretty
requests>=2.8.1
requests-futures>=0.9.5
futures>=2.2.0
httpretty
pyftdi
pylibftdi
pyserial
pyyaml