英文文档：
id(object)
Return the “identity” of an object. This is an integer which is guaranteed to be unique and constant for this object during its lifetime. Two objects with non-overlapping lifetimes may have the sameid() value.
CPython implementation detail: This is the address of the object in memory.
说明：
1. 返回对象的唯一标识符，用整数表示。在程序生命周期内，这个标识符常量是唯一的。
>>> a = 1 >>> id(a) >>> id(1.0) >>> a = 'some text' >>> id(a)
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