It seems that many, if not most people nowadays use IPython instead of the default Python interpreter. I’ve used it briefly in the past but, while I found a few features to be useful, such as the persistent command history and tab-completion, I found it to be otherwise quite bloated with features that I would never use (and which, furthermore, employ a strange and non-Python meta-syntax).
It appears to be an under-appreciated fact that you can run a script automatically when you launch the Python interpreter. I certainly did not know about it for some time. Using this feature, I’ve found that I can implement a few basic features in the standard Python interpreter that greatly improve its usage (for me), without going full hog with other features. I have just made the script available on Gitorious.
Many of its capabilities should come as no surprise to people who are familiar with Python: tab-completion, persistent history, etc. Others are non-standard and required a bit of hacking to get right: syntax-highlighted completion results, auto-indentation, and printable functions.
To use this script, just set the
PYTHONSTARTUP environment variable
to point to it, e.g. if the file is in
this in your
The script is compatible with both Python 2 and Python 3.
I highly recommend reading the code and modifying it to suit your tastes. Of course, if you hack up some cool new feature, I’d love to hear about it .
This comes as a bit of a side-effect: in order to implement some of
the functions in the start-up script, some modules had to be imported.
The benefit of this is that you won’t need to import some modules in
your interactive sessions,
Also, for Python 2, the
__future__. Additionally, the
pprint function is automatically
pprint pretty-prints objects, making it much easier to
view large lists or dicts, for example.
Your command history is saved between sessions, so you can recall
commands that you previously entered. Note that your Python 2 and
Python 3 histories are stored separately (though this is easy enough
to change if you don’t want that). By default, the command histories
are saved in
Colorized, history-aware prompts
Rather than the traditional
>>> (standard) and
prompts, this script provides prompts that show the current line in
the command history file. They are also colorized: the standard
prompt is green while the continuation prompt is yellow. These colors
are easily customized in the script.
>>> def foo(bar): ... print(bar)
After (you’ll have to imagine the colors in your mind):
> def foo(bar): (26)> print(bar)
Highlighted tab-completion of commands
When you are entering commands, you can hit the
<Tab> key to
complete a command.
That’s not terribly new and surprising. However, this script also highlights the completion results according to their syntactic function: modules in yellow, functions in blue, etc. It’s surprisingly useful.
Indentation keyboard shortcuts
Since indentation is so important in Python but since we are occupying
<Tab> with completion, I added some handy shortcuts to handle
indentation for you.
Ctrl-j will indent four spaces while
will unindent four spaces. These commands behave the way you would
expect: you can use them with the cursor residing anywhere in the
line, even in the middle of text (as opposed to having to move to the
beginning of the line and entering the spaces manually) .
To save you some keystrokes, your commands will be automatically
indented as necessary. For example, if you enter an
then the next line will automatically indent itself one level
inwards. If you then unindent a level, all lines after that will be
at the new indentation level. Note that the indentation will happen as
soon as you start typing, not as soon as the prompt appears like you
might expect .
This one’s a bit non-standard, so it bears some explaining. I found
that sometimes in my interactive sessions, I had forgotten the
specific details of a function definition. However, going back
through the command history would only show it one line at a time, and
in reverse at that. So, the start-up script provides a function
saved_function that allows you to recall and print the
definition of a function that was entered at the command-line
. Simply pass it the line in the command history where the
function definition will begin (i.e. the next line after the one where
the decorator is being entered).
> @saved_function(28) (27)> def foo(bar): (27)> print(bar) > # ...other stuff... # later... more work...hey, what does function foo do again? > print(foo) def foo(bar): print(bar)
readlinemodule is quite inflexible in its key-bindings. You cannot override some existing bindings for some reason. For example,
Ctrl-i, which would be a natural choice for adding to the indentation level, is inextricably tied to the
<Tab>key, causing it to always do completion, even if you try to re-bind it.
readlinemodule and, to my knowledge, there’s no way around it. Another side effect of this is that you will have to hit
<Enter>a couple times to end a block of code. Imagine you enter a one-line function. The function definition is at indentation level 0 and the line that comprises the body of the function will be at indentation level 1. After you enter the body line, if you start typing again, the text will be entered at level 1. However, if you just hit
<Enter>to finish the block, the
readlinemodule will accept that as "typing" and will first indent to level 1 before entering the line. The next time you hit
<Enter>, the previous blank line will be recognized by the auto-indentation code and the block will be completed. Again, to my knowledge, there is no way around this behavior (but I welcome any bug-fixes for it).
getsourcefunction of the