How can I do an "if run from ipython" test in Python?

This is probably the kind of thing you are looking for:

def run_from_ipython():
    try:
        __IPYTHON__
        return True
    except NameError:
        return False

The Python way is to use exceptions. Like:

try:
    from IPython.Debugger import Tracer
    debug = Tracer()
except ImportError:
    pass # or set "debug" to something else or whatever