理解"__repr__"

class aTest:
    def __repr__(self):
        return "This is an aTest class."
a = aTest()
print (a)
class bTest:
    pass
b = bTest()
print(b)

输出结果：

This is an aTest class.
<__main__.bTest object at 0x102a7f8d0>

所以，__repr__决定了直接打印一个实例时输出的字符串。