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pythonarrayslistbit-manipulation

Bits list to integer in Python

I have such list in Python: [1,0,0,0,0,0,0,0]. Can I convert it to integer like as I've typed 0b10000000 (i.e. convert to 128)? I need also to convert sequences like [1,1,0,0,0,0,0,0,1,0,0,0,0,0,0,0] to integers (here it will return 0b1100000010000000, i.e. 259). Length of list is always a multiple of 8, if it is necessary.

Solution

  • You can use bitshifting:

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

    This easily beats the "int cast" method proposed by A. R. S., or the modified cast with lookup proposed by Steven Rumbalski:

    >>> 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