Pimping out your .pythonrc.py

I don’t wanna be hatin’ on IPython, but I don’t use it. I often favor fairly extreme minimalism in computing. Why install something if you can accomplish the same (or good enough) with what you have available? IPython has quite a lot of features and syntactic-sugar, but it is overkill for my needs. Instead I’ve been slowly crafting my pythonrc.py to give the built-in Python shell color, tab completion, saving and searching a history, pretty printing, and the ability to start an external editor.

It should be said that this code is not especially interesting, and a lot of this is very straightforward readline configuration – but it seems that a lot of people are unfamiliar with the basics, so here is my set up.

There are two parts. The inputrc sets up the key-bindings and some completion options, and the pythonrc.py which does the rest.

You will almost certainly want to strip things out of my inputrc that you don’t use or enjoy, like vi-mode. Note the conditional for Python in case you want any key-bindings specific to the Python shell.

The inputrc should be somewhat self-explanatory. For the options that aren’t check out the GNU Bash Reference Manual. Also Google is your friend. For example if you want to use page-up and page-down to do completion from your history use the following two commands:

"\e[5~": history-search-backward
"\e[6~": history-search-forward

Now you can type in the first few characters of a previous command, hit your history-search-backward key and, voila, you get the full command. You can also search your history for a pattern using the normal keys for that – for vi-mode hit esc to get in Normal mode then press ? followed by the search term. (I don’t know the search command for the regular Emacs shell mode.)

A very cool thing about the inputrc is it will also affect other programs that utilize readline, such as bash and the shells for SQLite, PostgreSQL, and MySQL.

In order for the Python shell to run your pythonrc.py file on startup you need to set the PYTHONSTARTUP environment variable. Place the following line in one of your shell startup files:

export PYTHONSTARTUP=$HOME/.pythonrc.py

Now run the Python shell and you should see color and some startup messages!

If you are a Django developer and DJANGO_SETTINGS_MODULE exists in your environment, it will import all the models in your project and set up the Django test environment automatically. Try it!

Lastly a few Python shell tips

  • A great way to introspect an unfamiliar object is to type the object name followed by a dot then hit tab. You will see the methods and attributes for that object.

  • You can get the output from the last command run with the variable _ (underscore). For example:

    >>> {1:2, 3:4}
    {1: 2, 3: 4}
    >>> t = _
    >>> t
    {1: 2, 3: 4}
    
  • Use the built-in help() method to get more info on a function or module. For example:

    >>> import os
    >>> help(os)
    Help on module os:
    ...
    

If you have any other tips or fixes, please let me know!

blog comments powered by Disqus