[IPython-user] Evaluation of arbitrary expressions in the prompt string

Michael Scarpa M.Scarpa at uva.nl
Wed Sep 14 05:32:34 CDT 2005

Dear IPython users,

I have stumbled across the following problem: I would like to have 
IPython execute a given command (calling the method of a defined 
object) after every time I enter a new command at the prompt. I found 
the description of IPython's arbitrary expression execution in the 
prompt string in the online manual and thought this could do exactly 
what I need. Since the object is defined when I start IPython (in a 
python file loaded via "execfile" directive in the ipythonrc file), and 
I want the method of this object to be called after each command I 
issue, I thought that inserting something like "${object.method()}" in 
my input prompt string would do. Alas, I keep getting a NameException, 
claiming that the object is not defined. I made a test and replaced the 
above expression with "${globals().keys()}", and indeed, that object I 
try to call is not there. Even worse: nothing that is in my current 
namespace (e.g. all the objects instantiated in the file I load via 
"execfile" in my ipythonrc) is there!

In what namespace is the expression in the prompt string executed? And 
how can I insert objects into it, or better, merge it with the current 

Alternatively: Is there a better way to do what I am trying to do?

Thanks a lot in advance for any reaction.

Kind regards,

Michael Scarpa

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