methodcaller and attrgetter objects seem to be picklable, but in fact the pickling is erroneous: >>> import operator, pickle >>> pickle.loads(pickle.dumps(operator.methodcaller("foo"))) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: methodcaller needs at least one argument, the method name >>> pickle.loads(pickle.dumps(operator.attrgetter("foo"))) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: attrgetter expected 1 arguments, got 0 When looking at the pickle disassembly, it seems that the argument to the constructor is indeed not pickled. >>> import pickletools; pickletools.dis(pickle.dumps(operator.methodcaller("foo"))) 0: \x80 PROTO 3 2: c GLOBAL 'operator methodcaller' 25: q BINPUT 0 27: ) EMPTY_TUPLE 28: \x81 NEWOBJ 29: q BINPUT 1 31: . STOP highest protocol among opcodes = 2