We are doing quite some coding in Python lately (well, and also at spare time), and it is always nice to have the possibility of having the interactive interpreter to play with. But sometimes my mind refuses to stop working, so I wondered whether there would be a simple way of improving the overall user experience when using the stock Python interpreter without needing to install alternative ones like bpython, IPython or Reinteract. The idea is to have something a bit better without throwing in additional dependencies.

So I lurked a bit by the documentation and learnt about the PYTHONSTARTUP environment variable. Next step? Fired out $EDITOR and created a ~/.startup.py file with the following contents:

import readline, atexit, os, rlcompleter

historypath = os.path.expanduser("~/.pyhistory")
readline.parse_and_bind("tab: complete")

def save_history(historypath=historypath):
    import readline
    readline.write_history_file(historypath)

if os.path.exists(historypath):
    readline.read_history_file(historypath)

atexit.register(save_history)

del os, atexit, readline, save_history, historypath, rlcompleter

The most important thing is to bind the Tab key for completion. That complete function already comes bundled with the Python binding for readline (and compatibles), and will complete names for functions, variables, classes, methods, etc.

The rest of the snippet deals with saving the history of entered lines to a file when the interpreter is exited. The trick there is the historypath=historypath, to make that variable an upvalue. Being that way, we can clean up everything (last line) after initialization, so the interpreter will not get its global namespace poluted.

Finally, make PYTHONSTARTUP to be defined in every shell creation:

echo 'export PYTHONSTARTUP="$HOME/.startup.py"' >> .bashrc

Now re-launch your shell, type in python and enjoy your freshly-supercharged interpreter:

$ exec bash -l
$ python
Python 2.5.5 (r255:77872, Mar 20 2010, 05:19:32)
[GCC 4.4.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os. # tap TAB two-times here
Display all 224 possibilities? (y or n)