I'm developing a new application and my first in Python on the raspberry pi. Is there any disadvantage to using python 3.5 vs 2.7? The application will be strictly console not x11. Are all the modules available for 2.7 available for 3.5? [removed part about not being able to get latest version of pyserial using pip]
I would have expected
sudo pip3 intall --upgrade pyserial
to install the latest version but, having just tested it on my RPi, I find it doesn't work! It may be a temporary glitch but pypi.python.org seems to have been abandoned by its maintainers in favour of its replacement 'warehouse' However there are issues with database sorting versions (checkout bitbucket) This seems a bad thing for anyone thinking of using python!!
You can get the latest pyserial by downloading from https://pypi.python.org/pypi/pyserial/3.0.1 unzipping and running
sudo python3 setup.py install
On the issue of python2 v. python3 I think any disadvantages will be small compared with the fact that sooner or later python2 will stop being maintained. Where modules exist for python2 but not for python3 it's a good indication that you should look elsewhere. (I recently struggled to make a pi3d demo using Gtk that would work nicely with python2 and python3. The fact that documentation and general info on the web is ancient made me realise that Qt would be a much better option)