+
−#!/usr/bin/env python
+
−
+
−class Foo(object):
+
−  def __init__(self, mutable=['default']):
+
−    self.foo = mutable
+
−    self.foo.append(1)
+
−
+
−if __name__ == '__main__':
+
−  bar = Foo()
+
−  print len(bar.foo)
+
−  fleem = Foo()
+
−  print len(fleem.foo)
+
−  assert len(fleem.foo) == 2, "Don't use default mutable arguments!"