Q:

How do I find out what Python libraries are installed on my Mac?

I'm just starting out with Python, and have found out that I can import various libraries. How do I find out what libraries exist on my Mac that I can import? How do I find out what functions they include?
I seem to remember using some web server type thing to browse through local help files, but I may have imagined that!

A:

From the Python REPL (the command-line interpreter / Read-Eval-Print-Loop), type help("modules") to see a list of all your available libs.
Then to see functions within a module, do help("posix"), for example.  If you haven't imported the library yet, you have to put quotes around the library's name.

A:

For the web server, you can run the pydoc module that is included in the python distribution as a script:
python /path/to/pydoc.py -p 1234

where 1234 is the port you want the server to run at. You can then visit http://localhost:1234/ and browse the documentation. 

A:

Every standard python distribution has these libraries, which cover most of what you will need in a project.
In case you need to find out if a library exists at runtime, you do it like this
try:
    import ObscureModule
except ImportError:
    print "you need to install ObscureModule"
    sys.exit(1) # or something like that

