PBS, a new Python extension available for developers, aims to provide the best features of Bash with the flexibility of Python.  Far from "a collection of system commands implemented in Python," importing PBS provides a dynamic lookup mechanism that makes system programs available to a shell-style script.

Andrew Moffat provides several examples of how useful PBS can be, including this one dealing with Exceptions:

Exceptions are dynamically generated based on the return code of the command. This lets you catch a specific return code, or catch all error return codes through the base class ErrorReturnCode:

try: print ls("/some/non-existant/folder")
except ErrorReturnCode_2:
    print "folder doesn't exist!"
    create_the_folder()
except ErrorReturnCode:
    print "unknown error"
    exit(1)

-- Andrew Moffat

Other examples provided by Moffat on his GitHub page include:

• Executing Commands
• Piping
• Finding Commands
• Commandline Arguments
• Weirdly-names Commands

PBS requires Python 2.5.1 or higher and has been released under the Apache License 2.0.