4、迁移中的数据类型变化：int/long统一、range/xrange、map/filter/zip返回迭代器
从 Python 2 迁移到 Python 3，数据类型这块的变化，说实话，是很多老项目翻车的高发区。我当年接手一个金融风控系统的迁移，光是在 range 和 map 上就踩了好几个坑。今天咱们就把这三个核心变化掰开揉碎了讲清楚。
4.1 int 与 long 的统一：告别「大整数焦虑」
Python 2 里，整数分两种：int 和 long。前者是 32 位或 64 位，有上限；后者是「无限大」的，但会在数字后面带个 L 后缀。你想想看，写个 10000000000，Python 2 自动给你转成 10000000000L，看着就别扭。
Python 3 直接把它们合并了。现在只有一个 int，它本质上就是 Python 2 的 long。说白了，你再也用不着担心整数溢出了。
核心变化：Python 3 的 int 是任意精度整数，long 类型被彻底移除。
4.1.1 代码迁移示例
# Python 2 写法
a = 10 # int
b = 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