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In an assignment I am currently working on we need to work with bit vectors, but I am very unsure of how to do this in Python. They should be able to be from 4 bits to 20 bits. I have never worked with bit vector before, but I guess that one would one create arrays of unsigned bytes that you manipulated using the usual AND/OR/XOR operations.
The important restriction here is: I cannot rely on any libraries other than those supplied with standard Python.
I think I know how I would do this in C using arrays of 8 bit unsigned bytes: e.g. to turn the 18th bit of a zeroed array into a one, I would do something like my_bit_array[3] &= 1<<2
But since Python is dynamically typed and does not have a built-in array type, how would I go about doing this in a pythonic way?
And is it possible (how?) to express a bit vector of size 20? I am thinking of perhaps making a 24 bit / 3 byte vector and ignoring the 4 bits.
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A Bit Vector Class in Python, Version 1.1. The BitVector class is for a memory-efficient packed representation of bit arrays and for logical operations on such arrays. The core idea used in this Python script for bit packing is based on an internet posting by Josiah Carlson to the Pyrex mailing list.
A Python interface to the fast bitsets in Sage. Bitsets are fast binary sets that store elements by toggling bits in an array of numbers. A bitset can store values between 0 and capacity - 1 , inclusive (where capacity is finite, but arbitrary).
A bit array (also known as bit map, bit set, bit string, or bit vector) is an array data structure that compactly stores bits. It can be used to implement a simple set data structure. A bit array is effective at exploiting bit-level parallelism in hardware to perform operations quickly.
A vector is similar to an Array. A vector holds multiple number values. In Python, you can do operations on vectors using things like dot product and cross product, in linear algebra. These operations are used to efficiently manipulate data when creating neural networks and 3d rendering.
I'm surprised that no one has mentioned ints (or I guess long in Python 2). ints can be arbitrarily large, you can use bitwise operators on them, they're fast, and the code looks like bit twiddling code in C (I consider that to be an advantage).
x = 0 # empty
x |= 1<<19 # set bit 19
x &= ~(1<<19) # clear bit 19
x ^= 1<<19 # toggle bit 19
x = ~x # invert *all* bits, all the way to infinity
mask = ((1<<20)-1) # define a 20 bit wide mask
x &= mask # ensure bits 20 and higher are 0
x ^= mask # invert only bits 0 through 19
(x >> 19) & 1 # test bit 19
(x >> 16) & 0xf # get bits 16 through 20.
I've used this for bitvectors hundreds of bits long.
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