I have recently started learning Python and I have 2 questions relating to modules.
1) Using the help function
Get into the python prompt and type the following command:
>>>help("modules")
This will list all the modules installed in the system. You don't need to install any additional packages to list them, but you need to manually search or filter the required module from the list.
2) Using pip freeze
sudo apt-get install python-pip
pip freeze
Even though you need to install additional packages to use this, this method allows you to easily search or filter the result with grep command. e.g. pip freeze | grep feed.
You can use whichever method is convenient for you.