def __init__(self, fn):
''' generate a CallTree with the given function '''
assert callable(
fn), 'CallTree needs a function as its argument, not {}'.format(fn)
sio = StringIO()
p = Pdb(stdout=sio)
for i in range(512):
p.cmdqueue.append('s')
p.cmdqueue.append('q')
p.runcall(fn)
sio.seek(0)
self.target_fn = fn
self.pdb_text = sio.read()
