How to use pip3 for python 3.6 instead of python 3.5?

Your version of pip is inextricably linked to your version of Python, you cannot tell pip "use this Python" or "use that Python." If you have a version mismatch between pip3 (using Python 3.X) and python3 (being Python 3.Y), it means your problem is with multiple overlapping distributions of Python and a weirdly configured $PATH.

If you run pip3 --version it will tell you the site-packages directory and Python version number that pip3 is associated with.

If you run python3 and then execute >>> import site; site.getsitepackages(), it should print the site-packages directory your python3 is using.

If these do not match, you've got path problems and you'll need to post more information about what operating system you're on, what Python distributions you're using, and how you installed them.

Update/Summary of Comment Thread: Original poster had a distribution-bundled Python 3.6 installed alongside a self-installed Python 3.5. The pip3 on their path was associated with Python 3.6 (system Python), while the command python3 was associated with Python 3.5 (their self-installed Python). Resolution:

Run which -a python3 to find Python 3.5. Add the location of Python 3.5 to your $PATH. (Do it in .profile or .bash_profile to make it permanent.)

You can explicitly run the pip3 script with a particular Python version, by prefixing it with the appropriate python3.x command:

ldo@theon:~> pip3 --version
pip 9.0.1 from /usr/lib/python3/dist-packages (python 3.6)
ldo@theon:~> python3.5 $(which pip3) --version
pip 9.0.1 from /usr/lib/python3/dist-packages (python 3.5)

To install a package in the same version location that's associated with the version associated with python3, use the following:

python3 -m pip install [package]

to pick a specific version that you'd like your package to be associated with (so you're not guessing with the above):

python3.5 -m pip install [package]
python3.7 -m pip install [package]

Also, be careful because pip3 can point to different locations and may not necessarily match the location of the python3 binary. I just found that out when I did a pip3 install and it failed to import when running python3.

You can also explicitly call pip3.5, pip3.7, etc, but honestly I prefer using the python[version] -m pip install [package] method because I know that it will install the package in the location associated with whatever python3.x binary I'm using.