Python:为什么 `random.randint(a, b)` 返回一个包含 `b` 的范围?

2022-01-14 00:00:00 python random integer boundary

问题描述

random.randint(a, b) 会返回 [a, b] 范围内的整数，而不是 ，这对我来说总是很奇怪>[a, b-1] 像 range(...).

It has always seemed strange to me that random.randint(a, b) would return an integer in the range [a, b], instead of [a, b-1] like range(...).

这种明显的不一致有什么原因吗?

Is there any reason for this apparent inconsistency?

解决方案

我试图通过检查一些旧资源来了解这一点.我怀疑 randint 是在 Python 的长整数之前实现的:这意味着如果你想要一个包含 INT_MAX 的随机数，你需要调用random.randrange(0, INT_MAX + 1) 会溢出并导致参数为 (0, 0) 或 (0, INT_MIN) 取决于.

I tried to get to the bottom of this by examining some old sources. I suspected that randint was implemented before Python's long integer: meaning that if you wanted a random number that included INT_MAX, you would have needed to call random.randrange(0, INT_MAX + 1) which would have overflowed and resulted in arguments of (0, 0) or (0, INT_MIN) depending.

但是，甚至可以追溯到 Python 1.5.2 源代码，在 Lib/whrandom.py 我们看到:

However, looking as far back as even the Python 1.5.2 sources, in Lib/whrandom.py we see:

#
# Get a random integer in the range [a, b] including both end points.
# (Deprecated; use randrange below.)
#
def randint(self, a, b):
    return self.randrange(a, b+1)

whrandom.randint 在 2.0, 2.1, 2.2 和 2.3;但 random.randint 在 2.1，虽然在 2.2.

whrandom.randint was continued to be deprecated in 2.0, 2.1, 2.2, and 2.3; but random.randint was marked as deprecated in 2.1, although no longer marked as deprecated in 2.2.

另外，随机2.1 版中的 .py 是 random.randint 的文档字符串中第一个要注意的:

Also, random.py from version 2.1 is the first to note in random.randint's docstring:

def randrange(self, start, stop=None, step=1, int=int, default=None):
    """Choose a random item from range(start, stop[, step]).

    This fixes the problem with randint() which includes the
    endpoint; in Python this is usually not what you want.
    Do not supply the 'int' and 'default' arguments.
    """

比这更早的唯一可用源是0.9.1 源，并且据我所知，当时还没有实现 randint.

The only available source older than that is the 0.9.1 source, and as far as I can tell, randint was not implemented at that point.

因此，我得出结论，randint 包括端点的推理目前只有 Guido 本人知道；鉴于 Python 2.1 的文档字符串，听起来原因可能是一个简单的错误.

Thus, I conclude that the reasoning for randint including the endpoint is known to only Guido himself at this point; given the docstring from Python 2.1, it sounds like the reason may have been a simple mistake.

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