Added option (-c) to display cycles including uncollectable garbage.

mdboom · mdboom · commit b4d4aa7e50e3 · 2007-07-03T14:29:31.000Z
Displays the total number of Python objects in existence at each
iteration.

svn path=/trunk/matplotlib/; revision=3452
diff --git a/lib/matplotlib/cbook.py b/lib/matplotlib/cbook.py
@@ -844,6 +844,68 @@ def plot(self, i0=0, isub=1):
         show()
 
 
+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.
+    """
+    import gc
+    from types import FrameType
+
+    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("( tuple )")
+            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, { }, [])
+
 if __name__=='__main__':
     assert( allequal([1,1,1]) )
     assert(not  allequal([1,1,0]) )
