Functional way to replace reduce()

Question

In Python 3, reduce() has been moved to functools.reduce() and apparently it's better to use list comprehensions or plain loops for better readability.

I want to print the XOR'ed value of all elements in a list.

# My implementation with functools
from functools import reduce
print(reduce(lambda a, b: a^b, [1, 3, 2, 3, 4, 4, 5, 2, 1]))

And I have this:

# My implementation without functools
def XOR(x):
    ans = 0
    for i in x:
        ans = ans ^ i
    return ans

print(XOR([1, 3, 2, 3, 4, 4, 5, 2, 1]))

How can write a more functional version of this code without reduce()?

(Please provide references or code in Python 3, if any.)

Answer 1

Although Guido van Rossum didn't much care for reduce(), enough of the community did want it, which is why it was moved to functools and not removed outright. It is performant, and ideally suited to your use case. Just use it.

You can make your case faster and more readable by using operator.xor() to avoid the overhead of a new Python frame for a lambda:

from functools import reduce
from operator import xor

reduce(xor, [1, 3, 2, 3, 4, 4, 5, 2, 1])

Both xor() and reduce() are implemented in C. Calling back to the Python interpreter loop for the lambda is quite slow compared to calling another C function.

If you really must use a function, then use

def xor_reduce(values):
    result = 0
    for value in values:
        result ^= value
    return result

using in-place XOR, and better variable names.