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Fri, Oct. 16th, 2009, 10:26 am

This post unintentionally demonstrates that functional-style Python is ugly and bad.

Let us start at the top. At the beginning, it has some sample code which defines a multiple() function, which could be trivially inlined, resulting in code which looks like this (I'm doing all examples in Python 3):
print(sum(x for x in range(1, 1000+1) if x % 3 == 0 or x % 5 == 0))

There's no reason whatsoever to expand that out. This should be an early indication that maybe the code samples here aren't the greatest.

Moving on, there's getting the sum of all fibonacci numbers less than 4 million. This is done in the example using itertools and yield, resulting in a fair amount of ugly code. Here's how a sane person does it:
def fibsum():
	a, b, c = 0, 1, 1
	total = 0
	while c < 4000000:
		total += c
		a, b, c = b, c, b + c
	return total

Now that's much more readable, flexible, and maintainable.

Finally, there's the problem of finding the largest palindrome which is the product of two three digit numbers. Here's my solution, which contains less code, is much more readable, and oh yeah, I threw in an optimization to make it return almost instantly instead of having to crunch for a second:
def bigpalindrome():
	best = 0
	for i in range(999, 0, -1):
		if i * 999 < best:
			return best
		for j in range(999, i-1, -1):
			x = list(str(i*j))
			x.reverse()
			if int(''.join(x)) == i*j:
				best = i*j

Much better. I think these examples do a good job of exploding the idea that the functional style of programming is clearly better and the appropriate first thing to teach people. Obviously some people are being driven to write horribly contorted and ugly code because they started in a functional language when they switch a more, ahem, mainstream one.

Sat, Oct. 17th, 2009 08:41 pm (UTC)
stigant

>> Adding an if for it is completely trivial.
Sure, but missing the point. ie it makes your code less readable, maintainable, and flexible.

>>None of these examples have anything to do with thread safety,
I was providing that as an example of a way to extend the program's usefulness (ie flexibility). You will have a hard time implementing the fib seq as a list in a way that is thread safe because it will require state changes which will have to be surrounded by semaphores. With the functional/lazy approach you get thread safety for free, no extra effort - no need to embed it in the code. The alternative is to embed the fib seq generation code in your processing code (something I consider to be just as stupid as embedding thread safety) as you have done. Unfortunately, that requires that part of the program to be duplicated for every fib-seq consuming application.