Cookbook: Dynamic prompt

This assumes IPython 0.12

I used IPython to create a custom shell for a project at work. I wanted the prompt to show some status information about the state of the system it was controlling.

ED: I've changed these examples to use the config system. You can do the same things with an embedded instance of IPython .

First, we change the default ipython_config.py file, adding these lines:

 # _foobar will be the part of the prompt we control
 c.PromptManager.in_template = "[{_foobar}]\n[\#]>>> "
 c.PromptManager.in2_template = ".\D.>>> "
 c.PromptManager.out_template = "[\#]<<< "

Next, we prepare our variable, ensuring it has a `__str__()` method for the prompt formatter to call:

This code goes in a startup file. Create a file such as `foobar_prompt.py` in `profile_default/startup/`

 class FoobarPrompt(object):
     var = "foo"
     def __str__(self):
         if self.var.lower() in ["foo", "bar"]:
             return self.var
         else:
             return "UNKNOWN"
 _foobar = FoobarPrompt()
 
 del FoobarPrompt

Expected output:

$ ipython 

[foo]
[1]>>> _foobar.var = "blah"

[UNKNOWN]
[2]>>> _foobar.var = "BAR"

[BAR]
[3]>>> _foobar
[3]<<< <__main__.FoobarPrompt at 0x25c2f90>

[BAR]
[4]>>> 

You can also automatically set the state from the `pre_run_code_hook` (gets run every time code is executed) or the `pre_prompt_hook` (gets run just before the prompt is printed).

 def update_prompt(self):
     "Switch prompt between 'foo' and 'bar'."
     _foobar = self.user_ns['_foobar']
     _foobar.var = "foo" if (_foobar.var != "foo") else "bar"
 
 get_ipython().set_hook("pre_prompt_hook", update_prompt)

Finally, there are a number of built in prompt variables:

Built in prompt templates

Short	Long	Notes
%n, \#	{color.number}{count}{color.prompt}	history counter with bolding
\N	{count}	history counter without bolding
\D	{dots}	series of dots the same width as the history counter
\T	{time}	current time
\w	{cwd}	current working directory
\W	{cwd_last}	basename of CWD
\Xn	{cwd_x[n]}	Show the last n terms of the CWD. n=0 means show all.
\Yn	{cwd_y[n]}	Like \Xn, but show '~' for $HOME
\h	N/A	hostname, up to the first '.'
\H	N/A	full hostname
\u	N/A	username (from the $USER environment variable)
\v	N/A	IPython version
\$	N/A	root symbol ("$" for normal user or "#" for root)
\\	N/A	escaped '\'
\n	N/A	newline
\r	N/A	carriage return

On terminals supporting ANSI color switching, you can also use the following color variables:

# attributes of IPython.utils.coloransi.InputTermColors
{color.Black}           {color.Green}
{color.BlinkBlack}      {color.LightBlue}
{color.BlinkBlue}       {color.LightCyan}
{color.BlinkCyan}       {color.LightGray}
{color.BlinkGreen}      {color.LightGreen}
{color.BlinkLightGray}  {color.LightPurple}
{color.BlinkPurple}     {color.LightRed}
{color.BlinkRed}        {color.Purple}
{color.BlinkYellow}     {color.Red}
{color.Blue}            {color.White}
{color.Brown}           {color.Yellow}
{color.Cyan}            {color.Normal} (resets to terminal default)
{color.DarkGray}                       (try {color.normal} if above doesn't work)

So...

 c.PromptManager.in_template = "{color.LightGreen} \T {color.Yellow} \Y2 "

will produce a prompt with green time and yellow CWD.