fancycompleter: colorful Python TAB completion

What is is?

fancycompleter is a module to improve your experience in Python by adding TAB completion to the interactive prompt. It is an extension of the stdlib's rlcompleter module.

Its best feature is that the completions are displayed in different colors, depending on their type:

In the image above, strings are shown in green, functions in blue, integers and boolean in yellows, None in gray, types and classes in fuchsia. Everything else is plain white.

Other features

• To save space on screen, fancycompleter only shows the characters "after the dot". By contrast, in the example above rlcompleter shows everything prepended by "sys.".
• If we press <TAB> at the beginning of the line, a real tab character is inserted, instead of trying to complete. This is useful when typing function bodies or multi-line statements at the prompt.
• Unlike rlcompleter, fancycompleter does complete expressions containing dictionary or list indexing. For example, mydict['foo'].<TAB> works (assuming that mydict is a dictionary and that it contains the key 'foo', of course :-)).
• Starting from Python 2.6, if the completed name is a callable, rlcompleter automatically adds an open parenthesis (. This is annoying in case we do not want to really call it, so fancycompleter disable this behaviour.

Installation

First, install the module with pip:

pip install fancycompleter

Then, at the Python interactive prompt:

>>> import fancycompleter
>>> fancycompleter.interact(persist_history=True)
>>>

If you want to enable fancycompleter automatically at startup, you can add those two lines at the end of your PYTHONSTARTUP script.

If you do not have a PYTHONSTARTUP script, the following command will create one for you in ~/python_startup.py:

python -m fancycompleter install

On Windows, install automatically sets the PYTHONSTARTUP environment variable. On other systems, you need to add the proper command in ~/.bashrc or equivalent.

Note: depending on your particular system, interact might need to play dirty tricks in order to display colors, although everything should "just work". In particular, the call to interact should be the last line in the startup file, else the next lines might not be executed. See section What is really going on? for details.

How do I get colors?

If you are using PyPy or CPython 3.13+, you can stop reading now, as fancycompleter will work out of the box.

If you are using CPython on Linux/OSX (<3.13), fancycompleter installs pyrepl as a dependency, and you should also get colors out of the box. If for some reason you don't want to use pyrepl, you should keep on reading.

By default, in CPython line input and TAB completion are handled by GNU readline (at least on Linux). However, readline explicitly strips escape sequences from the completions, so completions with colors are not displayed correctly.

There are two ways to solve it:

• (suggested) don't use readline at all and rely on pyrepl
• use a patched version of readline to allow colors

By default, fancycompleter tries to use pyrepl if it finds it. To get colors you need a recent version, >= 0.8.2.

Starting from version 0.6.1, fancycompleter works also on Windows, relying on pyreadline. At the moment of writing, the latest version of pyreadline is 2.1, which does not support colored completions; here is the pull request which adds support for them. To enable colors, you can install pyreadline from this fork using the following command:

pip install --upgrade git+https://github.com/antocuni/pyreadline

Customization

To customize the configuration of fancycompleter, you need to put a file named .fancycompleterrc.py in your home directory. The file must contain a class named Config inheriting from DefaultConfig and overriding the desired values.

What is really going on?

The default and preferred way to get colors is to use pyrepl. However, there is no way to tell CPython to use pyrepl instead of the built-in readline at the interactive prompt: this means that even if we install our completer inside pyrepl's readline library, the interactive prompt won't see it.

The issue is simply solved by avoiding to use the built-in prompt: instead, we use a pure Python replacement based on code.InteractiveConsole. This brings us also some niceties, such as the ability to do multi-line editing of the history.

The console is automatically run by fancycompleter.interact(), followed by sys.exit(): this way, if we execute it from the script in PYTHONSTARTUP, the interpreter exits as soon as we finish the use the prompt (e.g. by pressing CTRL-D, or by calling quit()). This way, we avoid to enter the built-in prompt and we get a behaviour which closely resembles the default one. This is why in this configuration lines after fancycompleter.interact() might not be run.

Note that if we are using readline instead of pyrepl, the trick is not needed and thus interact() will simply returns, letting the built-in prompt to show up. The same is true if we are running PyPy, as its built-in prompt is based on pyrepl anyway.