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Comment by hvm | Hacker News Reader

I think it's a matter of taste or what you're used to. I find the first two examples clearer than the map/filter ones.

Are map and filter more concise? Yeah but only in this case. If you would need to do some processing, they would get messy fast because of a lambda.

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I work with a lot of people who have never drunk the functional koolaid, professionally. They have to do an extra mental step with map or filter - "oh map, that's where the first argument is applied to each item in the second - I think - perhaps the second argument is applied to the first, right, Stack Exchange". More explicit is clearer, then. 'Clear' like beauty, is subjective. But productivity isn't. And whatever my personal feelings, the productivity of the team wins.

On the second point. I agree. Python's lambdas are a code-smell, for me. Which I don't say lightly, I'm a Scheme/Lisp guy deep down. But they fundamentally work against the aesthetics of the Python language, imho. A local function declaration is much less fragile.

But I would say that as code complexity increases, in my experience, comprehensions don't last long either. They've a narrow range of applicability before you get a big block of spaghetti code. Then it is much better to define a local function and, essentially, 'map' it (even if that 'map' is done as comprehension). Of course, YMMV.

100% agree that lambdas fight python's aesthetics. On the expression complexity front I can definitely say it's easy to slowly increase their complexity until they're no longer readable. As a side note, comprehensions in Python (2 at least, not sure about 3) leak scope a bit which can lead to some really funky bugs if you're in a loop and absentmindedly use a loop variable in a comprehension.

  >> x = 5
  >> [x for x in range(10)]
  >> x # => 9

Yes, that was a pain. Particularly because it was only true of list comprehensions, not dict comprehensions or generators:

    Python 2.7.10 ...
    >>> a = 3
    >>> [a for a in range(10)]
    [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
    >>> a
    9
    >>> a = 3
    >>> list(a for a in range(10))
    [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
    >>> a
    3

Guido called it Python's 'dirty little secret'. It is fixed in Py3 though.

In my experience, the more complicated processing ends up being composed up of smaller units (that are testable), and then map/filter remain the most clear way of representing the iteration. Using lambdas for non-trivial process is just as bad as throwing that same complicated processing into a list comp.

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