Python – How to make a python, command-line program autocomplete arbitrary things NOT interpreter

autocompletecommand-linelinuxpythonunix

I am aware of how to setup autocompletion of python objects in the python interpreter (on unix).

Google shows many hits for explanations on how to do this.
Unfortunately, there are so many references to that it is difficult to find what I need to do, which is slightly different.

I need to know how to enable, tab/auto completion of arbitrary items in a command-line program written in python.

My specific use case is a command-line python program that needs to send emails. I want to be able to autocomplete email addresses (I have the addresses on disk) when the user types part of it (and optionally presses the TAB key).

I do not need it to work on windows or mac, just linux.

Best Solution

Use Python's readline bindings. For example,

import readline

def completer(text, state):
    options = [i for i in commands if i.startswith(text)]
    if state < len(options):
        return options[state]
    else:
        return None

readline.parse_and_bind("tab: complete")
readline.set_completer(completer)

The official module docs aren't much more detailed, see the readline docs for more info.

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Python – How to do a line break (line continuation) in Python

What is the line? You can just have arguments on the next line without any problems:

a = dostuff(blahblah1, blahblah2, blahblah3, blahblah4, blahblah5, 
            blahblah6, blahblah7)

Otherwise you can do something like this:

if (a == True and
    b == False):

or with explicit line break:

if a == True and \
   b == False:

Check the style guide for more information.

Using parentheses, your example can be written over multiple lines:

a = ('1' + '2' + '3' +
    '4' + '5')

The same effect can be obtained using explicit line break:

a = '1' + '2' + '3' + \
    '4' + '5'

Note that the style guide says that using the implicit continuation with parentheses is preferred, but in this particular case just adding parentheses around your expression is probably the wrong way to go.

Python – How to execute a program or call a system command

Use the subprocess module in the standard library:

import subprocess
subprocess.run(["ls", "-l"])

The advantage of subprocess.run over os.system is that it is more flexible (you can get the stdout, stderr, the "real" status code, better error handling, etc...).

Even the documentation for os.system recommends using subprocess instead:

The subprocess module provides more powerful facilities for spawning new processes and retrieving their results; using that module is preferable to using this function. See the Replacing Older Functions with the subprocess Module section in the subprocess documentation for some helpful recipes.

On Python 3.4 and earlier, use subprocess.call instead of .run:

subprocess.call(["ls", "-l"])

Best Solution

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Python – How to do a line break (line continuation) in Python

Python – How to execute a program or call a system command

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