Python中的位列表到整数

Question

我在 Python 中有这样的列表：[1,0,0,0,0,0,0,0]。我可以像输入 0b10000000 那样将其转换为整数（即​​转换为 128）吗？ 我还需要将[1,1,0,0,0,0,0,0,1,0,0,0,0,0,0,0] 之类的序列转换为整数（这里它将返回 0b1100000010000000，即 259）。 如果需要，列表的长度始终是 8 的倍数。

Answer 1

@Akavall 建议的最简单的方法是最快的。下面针对 mult_add_xor 的额外时序表明，python 中的位操作较慢，因为简单的加法“+ bit”比 xor “| bit”快，并且乘以 2 比移位“

import timeit

bit_list = [1, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0]


def mult_and_add(bit_list):
    output = 0
    for bit in bit_list:
        output = output * 2 + bit
    return output


def mult_and_xor(bit_list):
    output = 0
    for bit in bit_list:
        output = output * 2 | bit
    return output


def shifting(bitlist):
    out = 0
    for bit in bitlist:
        out = (out << 1) | bit
    return out


n = 1000000

a1 = mult_and_add(bit_list)
a2 = mult_and_xor(bit_list)
a3 = shifting(bit_list)

print('a1: ', a1, ' a2: ', a2, ' a3: ', a3)
assert a1 == a2 == a3

t = timeit.timeit('convert(bit_list)',
                  'from __main__ import mult_and_add as convert, bit_list',
                  number=n)
print("mult and add method time is : {} ".format(t))
t = timeit.timeit('convert(bit_list)',
                  'from __main__ import mult_and_xor as convert, bit_list',
                  number=n)
print("mult and xor method time is : {} ".format(t))
t = timeit.timeit('convert(bit_list)',
                  'from __main__ import shifting as convert, bit_list',
                  number=n)
print("shifting method time is : {} ".format(t))

输出：

a1:  49280  a2:  49280  a3:  49280
mult and add method time is : 0.9469406669959426 
mult and xor method time is : 1.0905388034880161 
shifting method time is : 1.2844801126047969 

Answer 2

这个怎么样：

out = sum([b<<i for i, b in enumerate(my_list)])

或以相反的顺序：

out = sum([b<<i for i, b in enumerate(my_list[::-1])])

Answer 3

我遇到了一种稍微优于 Martijn Pieters 解决方案的方法，尽管他的解决方案当然更漂亮。我其实对结果有点惊讶，但无论如何......

import timeit

bit_list = [1,1,0,0,0,0,0,0,1,0,0,0,0,0,0,0]

def mult_and_add(bit_list):
    output = 0
    for bit in bit_list:
        output = output * 2 + bit
    return output

def shifting(bitlist):
     out = 0
     for bit in bitlist:
         out = (out << 1) | bit
     return out

n = 1000000

t1 = timeit.timeit('convert(bit_list)', 'from __main__ import mult_and_add as convert, bit_list', number=n)
print "mult and add method time is : {} ".format(t1)
t2 = timeit.timeit('convert(bit_list)', 'from __main__ import shifting as convert, bit_list', number=n)
print "shifting method time is : {} ".format(t2)

结果：

mult and add method time is : 1.69138722958 
shifting method time is : 1.94066818592 

Answer 4

试试这个单行：

int("".join(str(i) for i in my_list), 2)

如果您关心速度/效率，请查看 Martijn Pieters 的解决方案。

Answer 5

你可以使用位移：

out = 0
for bit in bitlist:
    out = (out << 1) | bit

这很容易胜过 A. R. S. 提出的“int cast”方法，或 Steven Rumbalski 提出的带有查找的修改后的转换：

>>> def intcaststr(bitlist):
...     return int("".join(str(i) for i in bitlist), 2)
... 
>>> def intcastlookup(bitlist):
...     return int(''.join('01'[i] for i in bitlist), 2)
... 
>>> def shifting(bitlist):
...     out = 0
...     for bit in bitlist:
...         out = (out << 1) | bit
...     return out
... 
>>> timeit.timeit('convert([1,0,0,0,0,0,0,0])', 'from __main__ import intcaststr as convert', number=100000)
0.5659139156341553
>>> timeit.timeit('convert([1,0,0,0,0,0,0,0])', 'from __main__ import intcastlookup as convert', number=100000)
0.4642159938812256
>>> timeit.timeit('convert([1,0,0,0,0,0,0,0])', 'from __main__ import shifting as convert', number=100000)
0.1406559944152832

Answer 6

...或使用bitstring 模块

>>> from bitstring import BitArray
>>> bitlist=[1,0,0,0,0,0,0,0]
>>> b = BitArray(bitlist)
>>> b.uint
128