import gc
from types import FrameType
def print_cycles(objects, outstream=sys.stdout, show_progress=False):
"""
objects: A list of objects to find cycles in. It is often useful
to pass in gc.garbage to find the cycles that are
preventing some objects from being garbage collected.
outstream: The stream for output.
show_progress: If True, print the number of objects reached as they are
found.
"""
def print_path(path):
for i, step in enumerate(path):
# next "wraps around"
next = path[(i + 1) % len(path)]
outstream.write(" %s -- " % str(type(step)))
if isinstance(step, dict):
for key, val in step.items():
if val is next:
outstream.write("[%s]" % repr(key))
break
if key is next:
outstream.write("[key] = %s" % repr(val))
break
elif isinstance(step, list):
outstream.write("[%d]" % step.index(next))
elif isinstance(step, tuple):
outstream.write("[%d]" % list(step).index(next))
else:
outstream.write(repr(step))
outstream.write(" ->\n")
outstream.write("\n")
def recurse(obj, start, all, current_path):
if show_progress:
outstream.write("%d\r" % len(all))
all[id(obj)] = None
referents = gc.get_referents(obj)
for referent in referents:
# If we've found our way back to the start, this is
# a cycle, so print it out
if referent is start:
print_path(current_path)
# Don't go back through the original list of objects, or
# through temporary references to the object, since those
# are just an artifact of the cycle detector itself.
elif referent is objects or isinstance(referent, FrameType):
continue
# We haven't seen this object before, so recurse
elif id(referent) not in all:
recurse(referent, start, all, current_path + [obj])
for obj in objects:
outstream.write("Examining: %r\n" % obj)
recurse(obj, obj, { }, [])
