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Using optcomplete Conditionally

Author: Martin Blais <>
Date: 2004-01-28


Notes on adding conditionals for scripts to keep on working even without optcomplete.


Sometimes it is important for a particular script to be able to work without the presence of the non-standard optcomplete module. After that, if that is the only thing that is missing, the script is still able to do its work without completion.

This document contains little notes on how to do this but still take advantage of auto-generated completion if the module is available.


Note that if your shell binding hooks a program to the autocomplete function, the program will be invoked without arguments and you will see the output that calling it as such would generate, unless the program is written to handle this case by manually recognizing completion is being called for, e.g.:

elif 'COMP_LINE' in os.environ:
    return -1


You can import like this:

    import optcomplete
except ImportError:
    optcomplete = None

Then, further one, you can use a global conditional for the completion code:

if optcomplete:


if optcomplete:
    optcomplete.autocomplete(parser, ['.*\.tar.*'])

With Subcommands

Importing, with a base class for commands:

    import optcomplete
    CmdComplete = optcomplete.CmdComplete
except ImportError:
    optcomplete, CmdComplete = None, object

Then you can use the same conditional:

class CmdCompleting(CmdFoo):


    if optcomplete:
        completer = .......

    def addopts( self, parser ):
        CmdFoo.addopts(self, parser)
        opt = parser.add_option(....
        if optcomplete:
            opt.completer = .....

You can also check for completions manually and return nothing if the invocation is from completion:

# subcommand completions
if optcomplete:
    scmap = {}
    for sc in subcmds:
        for n in sc.names:
            scmap[n] = sc

    listcter = optcomplete.ListCompleter(scmap.keys())
    subcter = optcomplete.ListCompleter(
        ['some', 'default', 'commands', 'completion'])
        gparser, listcter, None, subcter, subcommands=scmap)
elif 'COMP_LINE' in os.environ:
    return -1