Explain Python entry points?

I’ve read the documentation on egg entry points in Pylons and on the Peak pages, and I still don’t really understand. Could someone explain them to me?

Answer

An “entry point” is typically a function (or other callable function-like object) that a developer or user of your Python package might want to use, though a non-callable object can be supplied as an entry point as well (as correctly pointed out in the comments!).

The most popular kind of entry point is the console_scripts entry point, which points to a function that you want made available as a command-line tool to whoever installs your package. This goes into your setup.py script like:

entry_points={
    'console_scripts': [
        'cursive = cursive.tools.cmd:cursive_command',
    ],
},

I have a package I’ve just deployed called cursive.tools, and I wanted it to make available a “cursive” command that someone could run from the command line, like:

$ cursive --help
usage: cursive ...

The way to do this is define a function, like maybe a cursive_command function in the file cursive/tools/cmd.py that looks like:

def cursive_command():
    args = sys.argv[1:]
    if len(args) < 1:
        print "usage: ..."

and so forth; it should assume that it’s been called from the command line, parse the arguments that the user has provided, and … well, do whatever the command is designed to do.

Install the docutils package for a great example of entry-point use: it will install something like a half-dozen useful commands for converting Python documentation to other formats.