CODEWITHSUNDEEP
python
Sir DrinksCoffeeALot
Sir DrinksCoffeeALot

Reputation: 633

How to apply bitwise-like XOR between lists of different lengths?

What i would like to do is to initialize an array which has 5 elements set to 0 and then copy the other array to the first one, something like this:

a = [0, 0, 0, 0, 0]
b = [1, 2, 3]
print a | b
[1, 2, 3, 0, 0]

Is there any pythonic way in doing so except:

for i, x in enumerate(b):
    a[i] = x

Edit:

I forgot to mention that buffer a will always be filled with plain zeroes at the beginning and condition len(b) < len(a) is always true, also in each case buffer a will always start getting overwritten from index 0.

Ill explain why i need this kind of behaviour in the first place, basicly I have a raw 256-byte UDP frame. Buffer a corresponds to bytes 16-31 in the frame. Depending on some conditions, those bytes will either be overwritten or be set at 0, length of b is always 12.

def foo(b=12*[0]):
    a = 16*[0]
    return a[:12] = b[:]

Upvotes: 0

Views: 554

Answers (4)

Mika72
Mika72

Reputation: 411

Something like this (Note: XOR operator is ^ ?

import itertools

a = [0, 0, 0, 0, 0]
b = [1, 2, 3]

def safeXOR(arr1, arr2):
    return list((x ^ y for (x, y) in itertools.zip_longest(arr1, arr2, fillvalue=0)))

print(safeXOR(a,b))

Upvotes: 0

Selcuk
Selcuk

Reputation: 59425

Why waste time defining a in the first place? You can simply append the correct number of 0s to b instead:

>>> b = [1, 2, 3]
>>> a = b + [0] * (5 - len(b))
>>> a
[1, 2, 3, 0, 0]

Upvotes: 1

Samuel GIFFARD
Samuel GIFFARD

Reputation: 842

This works in Python 2:

import itertools
a = [0, 0, 0, 0, 0]
b = [1, 2, 3]
g = (l | r for (l, r) in itertools.izip_longest(a, b, fillvalue=0))
print list(g)

And this in Python 3:

import itertools
a = [0, 0, 0, 0, 0]
b = [1, 2, 3]
g = (l | r for (l, r) in itertools.zip_longest(a, b, fillvalue=0))
print(list(g))

I created a generator g but if you know in advance you want all values of it already, then it's okay to have a list comprehension right away instead.

This is the doc for zip_longest: https://docs.python.org/3/library/itertools.html#itertools.zip_longest

Directly with the list comprehension (py3):

import itertools
a = [0, 0, 0, 0, 0]
b = [1, 2, 3]
g = [l | r for (l, r) in itertools.zip_longest(a, b, fillvalue=0)]
print(g)

Upvotes: 1

Ignacio Vazquez-Abrams
Ignacio Vazquez-Abrams

Reputation: 799210

>>> a[:len(b)] = b[:]
>>> a
[1, 2, 3, 0, 0]

Upvotes: 3

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