A Python development environment is a folder which you keep your code in, plus a "virtual environment" which lets you install additional library dependencies for that project without those polluting the rest of your laptop.
mkdir my-new-python-project
cd my-new-python-project
virtualenv --python=python2.7 venv
# This will create a my-new-python-project/venv folder
touch .gitignore
subl .gitignore
# Add venv to your .gitignore
Now any time you want to work on your project, you need to "activate your virtual environment". Do that like this:
cd my-new-python-project
source venv/bin/activate
You can tell it is activated because your terminal prompt will now look like this:
(venv) computer:my-new-python-project user$
Note the (venv) bit at the start.
Once it is activated, any time you run the "python" or "pip" commands it will be running the special custom versions in your venv folder.
You could also run them without activating the virtual environment like this:
venv/bin/python
venv/bin/pip
To install new python libraries, use pip like this:
pip install requests
pip install ipython
It's always a good idea to install ipython.
Here's how to sign the Python interpreter on OS X so it won't keep asking for network port permission: https://gist.github.com/simonw/68d19a46e8edc2cd8c68