Online Modification of Python Code

[malv]

I am involved in a major scientific algorithm design problem in which
simulation of the underlying physics and visualization play an
important role. Algorithm adaptation from run to run often involves few
lines of code. The setup of the system's state requires quite a bit of
processing time and rapidly becomes a real drag on the experimentation
sessions.

It would be very nice if Python would allow 'online' code modification
from the IDE, roughly analogous to VisualBasic (this is the only thing
I like in VB). Some reply that such a feature is unnescessary because
of unittest. This does not hold at all for a project like this wherby
the problem is not really to debug and veryfy program code.

Can anybody recommend a practical ad hoc solution to such problem?
Thanks all.