Python，len和整数的大小 [英] Python, len, and size of ints

问题描述

因此，当某事物的长度接近1 << 32（int的大小）时，cPython（2.4）会有一些有趣的行为。

So, cPython (2.4) has some interesting behaviour when the length of something gets near to 1<<32 (the size of an int).

r = xrange(1<<30)
assert len(r) == 1<<30

没问题，但是：

r = xrange(1<<32)
assert len(r) == 1<<32
ValueError: xrange object size cannot be reported`__len__() should return 0 <= outcome

Alex的 wowrange 也有这种行为。 wowrange（1<<< 32）.l 没问题，但 len（wowrange（1<< 32））很糟糕。我猜这里有一些浮点行为（被视为负面）行动。

Alex's wowrange has this behaviour as well. wowrange(1<<32).l is fine, but len(wowrange(1<<32)) is bad. I'm guessing there is some floating point behaviour (being read as negative) action going on here.

1. 这里究竟发生了什么？ （这在下面已经很好地解决了！）


2. 我该如何解决这个问题？多头？

1. What exactly is happening here? (this is pretty well-solved below!)
2. How can I get around it? Longs?

（我的具体应用是 random.sample（xrange（1<< 32），ABUNCH）） 如果有人想直接解决这个问题！）

(My specific application is random.sample(xrange(1<<32),ABUNCH)) if people want to tackle that question directly!)

推荐答案

cPython假设列表适合内存。这扩展到行为类似于列表的对象，例如xrange。实质上， len 函数需要 __ len __ 方法返回可转换为 size_t <的内容。 / code>，如果逻辑元素的数量太大，即使这些元素实际上不存在于内存中也不会发生。

cPython assumes that lists fit in memory. This extends to objects that behave like lists, such as xrange. essentially, the len function expects the __len__ method to return something that is convertable to size_t, which won't happen if the number of logical elements is too large, even if those elements don't actually exist in memory.

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