On 2020-05-30 23:52, evan.schal...@gmail.com wrote:
I frequently use binary as bool placeholders and find myself filtering lists
based on those bools, this seems to have a similar semantic meaning as the bit
wise ^ or __xor__ operator and could add syntactic sugar to the base list class.
Use Case:
Controlling a stepper at half-step has the following cycle steps:
CYCLE = [
[1,0,0,0],
[1,1,0,0],
[0,1,0,0],
[0,1,1,0],
[0,0,1,0],
[0,0,1,1],
[0,0,0,1],
[1,0,0,1],
]
which can be represented as follows:
CYCLE = [
1<<3,
1<<3|1<<2,
1<<2,
1<<2|1<<1,
1<<1,
1<<1|1<<0,
1<<0,
1<<3|1<<0
]
or more cleanly:
CYCLE = [8, 12, 4, 6, 2, 3, 1, 9]
Or more clearly:
CYCLE = [
0b1000,
0b1100,
0b0100,
0b0110,
0b0010,
0b0011,
0b0001,
0b1001,
]
on a raspberrypi, using (for illustration's sake) GPIO pins 1,2,3,4 I'd like to
use the __xor__ method (currently not implemented) to perform the bit-wise
filter as follows:
Bit-masking is done with a bitwise AND, so I'd expect the __and__ method
would be used. The __xor__ method would be for bit-toggling.
class MyList(list):
def __init__(self, *args):
super().__init__(args)
def __xor__(self, num):
return [self[i] for i in [-index-1 for index, i in
enumerate(bin(num)[:1:-1]) if i !='0']][::-1]
PINS = MyList(1,2,3,4)
PINS ^ 8
# [1]
PINS ^ 12
# [1, 2]
PINS ^ 4
# [2]
PINS ^ 6
# [2, 3]
PINS ^ 2
# [3]
PINS ^ 3
# [3, 4]
PINS ^ 1
# [4]
PINS ^ 9
# [1, 4]
The need here isn't strictly pi/stepper related; I've run into this several
times in the past when evaluating combinations * permutations of items where a
bitwise filter would be useful.
Do you really need a class for this?
CYCLE = [
0b1000,
0b1100,
0b0100,
0b0110,
0b0010,
0b0011,
0b0001,
0b1001,
]
PINS = [1, 2, 3, 4]
def bit_filter(pins, bits):
return [pin for pin, bit in zip(PINS, format(bits, '04b')) if bit
== '1']
bit_filter(PINS, 0b1000)
# [1]
bit_filter(PINS, 0b0100)
# [2]
bit_filter(PINS, 0b0110)
# [2, 3]
bit_filter(PINS, 0b0010)
# [3]
bit_filter(PINS, 0b0011)
# [3, 4]
bit_filter(PINS, 0b0001)
# [4]
bit_filter(PINS, 0b1001)
# [1, 4]
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