# The cycle GC collector can be executed when any GC-tracked object is # allocated, e.g. during a call to PyList_New(), PyDict_New(), ... # Moreover, it can invoke arbitrary Python code via a weakref callback. # This means that there are many places in the source where an arbitrary # mutation could unexpectedly occur. # The example below shows list_slice() not expecting the call to # PyList_New to mutate the input list. (Of course there are many # more examples like this one.) import weakref class A(object): pass def callback(x): del lst[:] keepalive = [] for i in range(100): lst = [str(i)] a = A() a.cycle = a keepalive.append(weakref.ref(a, callback)) del a while lst: keepalive.append(lst[:]) SIMPAN PERUBAHAN