Is it a bad practice writing long one-liner code?

Question

I found myself keep writing pretty long one-liner code(influenced by shell pipe), like this:

def parseranges(ranges, n):
    """
    Translate ":2,4:6,9:" to "0 1 3 4 5 8 9...n-1"
               == === ==      === ===== =========
    """
    def torange(x, n):
        if len(x)==1:
            (x0, ) = x
            s = 1 if x0=='' else int(x0)
            e = n if x0=='' else s
        elif len(x)==2:
            (x0, x1) = x
            s = 1 if x0=='' else int(x0)
            e = n if x1=='' else int(x1)
        else:
            raise ValueError
        return range(s-1, e)
    return sorted(reduce(lambda x, y:x.union(set(y)), map(lambda x:torange(x, n), map(lambda x:x.split(':'), ranges.split(','))), set()))

I felt ok when I written it.
I thought long one-liner code is a functional-programming style.
But, several hours later, I felt bad about it.
I'm afraid I would be criticized by people who may maintain it.
Sadly, I've get used to writing these kind of one-liner.
I really want to know others' opinion.
Please give me some advice. Thanks

Answer 1

I would say that it is bad practice if you're sacrificing readability.

Answer 2

It is common wisdom that source code is written once but read many times by different people. Therefore it is wise to optimize source code for the common case: being read, trying to understand.

My advice: Act according to this principle. Ask yourself: Can anybody understand any piece of my code more easily? When the answer is not a 100% "No, I can't even think of a better way to express the problem/solution." then follow your gut feeling and reformat or recode that part.