python2和3中zip的差异(坑)

class Foo(object):
    def __init__(self):
        self.items = range(3)
    def __getitem__(self, i):
        print('__getitem__', i)
        return self.items[i]
foo1 = Foo()
foo2 = Foo()
print(zip(foo1, foo2))
# for s1, s2 in zip(foo1, foo2):
#     print(s1, s2)

# 输出：
# 提前已经遍历了一遍，组成新的列表了
('__getitem__', 0)
('__getitem__', 0)
('__getitem__', 1)
('__getitem__', 1)
('__getitem__', 2)
('__getitem__', 2)
('__getitem__', 3)
[(0, 0), (1, 1), (2, 2)]

# 输出：
<zip object at 0x7f96933f9648>