将一个巨大的数乘以random（）（Python）

Question

问题：生成大型二进制字符串（长度2000+）。快做，因为这个generateRandom（）函数在算法中将被调用300000次。在

尝试的解决方案：生成3或4个二进制数并将它们相加500次。这太慢了。在

打一个电话给随机。随机（）再乘以一个很大的数。转换成二进制一次就可以了。这适用于较小的数字，但由于二进制字符串必须具有一定的长度，因此要转换为二进制的数字必须非常大（2**len（binString））。在

当前代码（适用于较小的数字）：

binaryRepresentation = ''

binaryRepresentation += bin(int(random.random() * (2 ** binLength)))[2:].zfill(binLength)

我需要帮助修复的错误：此调用抛出一个“long int too large to convert to float”，其中包含大量数字。有没有一种方法可以使整个算法更有效，或者使这个大的数能够转换成一个浮点数？在

谢谢你！

Answer 1

random.randrange真的太慢了吗？让我们看看它到底有多慢。在

import random

word_size = 2048
word_max = 2 ** word_size

def random_bits(n):
    """
    Return a string consisting of `n` zeroes and ones (chosen randomly).
    """
    def words():
        s, m, r = word_size, word_max, n % word_size
        for _ in range(n // s):
            yield bin(random.randrange(m))[2:].zfill(s)
        yield bin(random.randrange(2 ** r))[2:].zfill(r)
    return ''.join(words())

>>> from timeit import Timer
>>> Timer(lambda:random_bits(2000)).timeit(number=300000)
9.680696964263916

对于选择6亿随机位来说，10秒似乎不是一个荒谬的时间。所以也许你可以多说一下你的速度要求。这真的太慢了吗？在

Answer 2

从J.F.Sebastian对二进制字符串（其中包含0和1字符的字符串）的回答：

>>> import random
>>> r = random.SystemRandom()
>>> bin(r.getrandbits(2000))[2:].zfill(2000)
'00010110001101100011000011001011011000010001010111000001111001001111010110010110011011110011101101100001111000011111010110100110011011110011111110010111111001110110011011011111011101000010101001001000100010001011011100011101100101010110001101101100100000001001010001101100110001100001101101010010001000010010010101100110100000001001001101000110001011111111111010011111111011001000100011001011011100010100010000010011100100011111011110111101010001001111011010101101010000110110010011000101111110000101001111100111111101101101110001100111011110011001000110110011101001010111100110000111000110011010000000111011001011100000100100111011110111101001110001110010010101100110000111001011100101111110100000100101011000110100111111001100111001000000111010000000101001111011111101111111101101011010010001101101101010011000100101000111000100100011010100111101111010001011110100100011111101101000111011100010000111000111110100001100111010001001010100001010111100001001010110010010100010011010010010011000000011010111110001100001100110101111011100010100100101000101000111110011111011011011111101011001001111010110000101100011111000111010100001000000101111011010011010011101011110000101011011110001111111101100000100000110111100011010110000111110110010100010010111111110010000000100001011110011100001001110110111100001101000011101011011101110001001001110011111111010001000100011010000110011000000000011111011011011101011010010001000101001011111110110000011000000000010101101111100011001010011100010010110111011001001011011010101111011101000001000011110010011111000011001110000100100111010000011100111110101110111010010101110010111100011111001101010010010000001010110011110001110010011011001110011000010010111111100101101100110111100001101100001100000101110000000011111010011000010000000011001101000001001000101001010100001110001011111110100110111000101011101111110010110001111111010100000100011011110011100010000000101001011100000010101101110110001110010111010000111101110100001100101000101010000110111011001001011'
>>> bin(r.getrandbits(2000))[2:].zfill(2000)
'11111011011010000011111101101101001110101011100110100011111011101101111100110001000110110100101010101000110010000101010100011111100111100010000001011011101100011101000001100101000101000010010000001111110101010011001110001001010011000011010100011111110111110010100000111011000000110000100000000110101101101111001101100000010010000100101001111100101010011101011010111110010001111111100101011110001101100111010010101110111000001000100101111011010001111001001010010000011100111101101101111101111010101100001000110011100110010110010101101001011000010101011111010010111000000100101100000100000010010000001000000001110010010100100111001011011111100111111001100000111111110011100001000111111110110001000010010110101100100001000001011110110100000111010101100111111010011111011111011000100101010111111000110111001001100011101101001000100110011001011101100010011010101111000011011111110001010110100100100001010100100100110101100111011110101001001111000010001101001010111111110011110111011111010001110011001000000100000101100001001100101000010011001101001110000101100000110000110101110011000010111110100100100100110010111110011101001000100111110011001101010000101100010011110100100110000111010111001000001101010101000001111001110010111000000101111101000110100101101000100000101100100110111101100010011110111011010111000111111100001110000100111001110001010101111000111100000011111111111110110100011000000111010100111011011100100010110100010110001111010110010100101111010111101110011010110100100010001001001110010110100111010010111001011101100000010011000110011011011010001100010000000010110011101101000111101000011101100001010001010001010111111110101100001110010000001010000000011000000000101111001001100100010110010000000101001010011110110111101111001110001001110111101011111111010101101011101010010111101000000010000101010100000101111010011010001001001101000001001011010110000000000111010001111001110100110000100011110100110110010011000111110100011000110001100001101101001010110001001001001101000011011101001010'
>>> bin(r.getrandbits(2000))[2:].zfill(2000)
'00100010111111011100001001000010100100101000100010101010100001011100101010100000000011111000001001011101010010010000101111111001101101100101011011001011110001001111101011101000101101000001000000110010011001110010101100101000011111001111111011011010001010010000011000000010011001101000100101000001001101001100010100000100100110000010110101011101011111010000010110011001101010010010000111001101101101001001100101111001101110111111111000011000001011011100111010011101001100011101011001110010111101011111010100101101010001011011001001010001111011100100101100100011111010010011110010011101100101001100111011011110011101010101010011001100000100110000001001111001111010011110110110001100110111011011111001110101000100100000011101001100111001100010001101010110000110010101010100011011101101010010100011111100001100100011010111000001011000101110100001111111001001111111101001000000011110110001010101001110110011000010101011010111111011010000011000000111110001110111111110110001110101011000010101001111110111101101010000111000011001111110101000001000011110000101011011001001000100010000110000110011100000100110100101011010011000110001010000101001110101111000110101001010010101000100011010101001110101101111010010101000011111101110110100101000110011010100010110110101010111001010110111011000000010001000110010011000011011110101101000111111101110100100011100000011110100000110111001001101110000011001101101011001000000101001110110011101111111010000000101111011100011010110111110000000001110101101100001001000001010000100101001111110110101000000101101111010010110000111101111011111100001111010001000100110111011010100110111011101011110001001001010100010101011001100100110101101111010011110001010011110000100100011101100101000000001011001010100101010011000011000100001011010010001010100001110101101100000010101011111010011000000000100100000000001011110101011101100101100010110101000111001010000001011000010001111101011111000011100101101110111110000011001000001101010001010000111001100101100111000111000001000000000'

根据这个基准：

^{pr2}$

结果是Took 12.32s

不进行任何字符串转换就得到随机位（只有r.getrandbits(2000)）就花了7.77s，所以如果你能找到一种将随机位用作long的方法，那么你可以节省一些时间。在

使用os.urandom(250)重新运行基准测试（无需额外处理）只需3.59s，因此这似乎是最快的选择。在

Answer 3

衡量它是否足够快，以你的目的，“随机性”可能会减少你称之为：^{}。它产生一个二进制字符串aka bytes。在

为了避免“long int too large To convert To float”错误，不要使用float。在

如果需要一个带有k随机位的整数而不是二进制字符串：

import random
r = random.SystemRandom()

n = r.getrandbits(2000) # uses os.urandom() under the hood

要获取字符串“0”和“1”，请执行以下操作：

^{pr2}$

注意：如果不使用getrandbits，则不能将randint/randrange用于大数：

import random

class R(random.Random):
    def random(self): # override random to suppress getrandbits usage
        return random.random()

r = R()
r.randrange(2**2000) # -> OverflowError: long int too large to convert to float

b2a逯宾

^{} extension允许直接从bytestrings创建二进制字符串（“01”），而无需创建中间的Python整数。它比纯Python类似物快3-20倍：

def b2a_bin_bin(data):
    return bin(int.from_bytes(data, 'big', signed=False)
               )[2:].zfill(len(data)*8).encode('ascii', 'strict')

def b2a_bin_format(data):
    n = int.from_bytes(data, 'big', signed=False)
    return "{:0{}b}".format(n, len(data)*8).encode('ascii', 'strict')

用法：

>>> import os
>>> from b2a_bin import b2a_bin
>>> b2a_bin.b2a_bin(b'\x0a')
b'00001010'
>>> b2a_bin(os.urandom(5))
b'1001111011000011111001110010000101111010'