On Linux or MacOS:

python -m ensurepip --upgrade

If you want to install pip for Python 3, replace python with python3.

See https://pip.pypa.io/en/stable/installation/ for more details.

UPDATE: This is no longer necessary as of Python3.4. pip3 is installed as part of the general Python3 installation.

I ended up posting this same question on the python mailing list, and got the following answer:

# download and install setuptools
curl -O https://bootstrap.pypa.io/ez_setup.py
python3 ez_setup.py
# download and install pip
curl -O https://bootstrap.pypa.io/get-pip.py
python3 get-pip.py

Which solved my question perfectly. After adding the following for my own:

cd /usr/local/bin
ln -s ../../../Library/Frameworks/Python.framework/Versions/3.3/bin/pip pip

So that I could run pip directly, I was able to:

# use pip to install
pip install pyserial

or:

# Don't want it?
pip uninstall pyserial

well, packages for OSX may include packages for python.

pip is a packager for the python world - you should only ever be able to install python-things with it; homebrew is a package manager targetted at OSX; it doesn't impose any restrictions onto what software you can install with it - since python is a subset of software.

installing things with brew will install them into /usr/local/;

installing things with pip will fetch packages from the Python Package Index, and it will install them in a place where your python interpreter will find them: either into your home directory (e.g. ~/.local/lib/python2.7/site-packages/) or in some global search-path of your python interpreter (e.g. /usr/local/lib/python2.7/dist-packages/)

if you have installed the python interpreter via brew, then chances are high that any python-package installed via brew will be usable out of the box.

Maybe it is time to consider using virtualenv. Virtualenv creates self-contained python environments using the python version you specify. After activating the new virtual environment, everything you install using pip goes under that environment. This helps avoid situations like the one you described.

E.g. create and activate a new python environment using the default python:

# create environment
$ virtualenv --distribute myproject
New python executable in myproject/bin/python
Installing distribute...done.
Installing pip...done.

# activate environment
$ . ./myproject/bin/activate

# check default python
(myproject)$ which python
/Users/me/myproject/bin/python

It is suggested to use the --distribute options to indicate that distribute should be used for installing packages in the new environment instead of (the older) setuptools. After activation your command prompt changes to indicate which python environment is active.

Now install some package. The files will go into myproject directory:

# install django
(myproject)$ pip install django
...

# search for django dir
(myproject)$ find myproject -iname django
myproject/lib/python2.7/site-packages/django

Finally, deactivate:

# deactivate and check for default python
(myproject)$ deactivate
$ which python
/usr/bin/python

To create an environment using a non-default version of python:

$ virtualenv --distribute -p /path/to/custom/python mynewproject

By default virtualenv will copy to the new environment any packages installed for the python version you use to bootstrap it. To prevent this and create an empty environment use the --no-site-packages option. This is especially useful to create environments which can be exactly replicated e.g. from development to production.

Update: As of version 1.7 --no-site-packages has become the default behaviour of virtualenv.

If you want more details, there are plenty of tutorials and blog posts online. E.g.:

1. Notes on using pip and virtualenv with Django. (most of the post is not django-specific)
2. Working with virtualenv.

Give it a try and I'm sure you'll stick with it.

Note: Make sure that your executable scripts do not have the python interpreter hardcoded. I.e. their first line should be #!/usr/bin/env python and not something like #!/usr/bin/python.