I get the correct output only when I add another return value in Python3.x

Question

Sorry for the unspecific title, but I was not able to explain it better.

I have this python code:

def longestWord_with_recursion(wrds):
    if type(wrds) == str:
        return len(wrds),wrds
    return max([longestWord_with_recursion(x) for x in wrds])

(...)

words = [list of words]
print(longestWord_with_recursion(words))

The return with len(wrds),wrds gives me the following:

(11, 'programming') #programming is the correct answer

However, since I only want to return the word, I replace the return with return wrds, which gives me the following:

you #another word in the list, but the wrong one

Why does this happen? Why does it give me the correct word if I add another return value but not if I only return this one? And how could one fix this?

E: The list of words is:

['The', 'Scandal', 'of', 'education', 'is', 'that', 'every', 'time', 'you', 'teach', 'something', 'you', 'deprive', 'a', 'student', 'of', 'the', 'pleasure', 'and', 'benefit', 'of', 'discovery', 'Seymour', 'Papert', 'born', 'February', '29', '1928', 'died', 'July', '31', '2016', 'If', 'debugging', 'is', 'the', 'process', 'of', 'removing', 'bugs', 'then', 'programming', 'must', 'be', 'the', 'process', 'of', 'putting', 'them', 'in', 'Edsger', 'W', 'Dijkstra']

Hint: If you don't return the len(wrds), what would your max function do? — justhalf
– justhalf, Commented Nov 27, 2017 at 21:51

Prune · Accepted Answer · 2017-11-27 22:00:06Z

1

When you return only the word, the list you form with your recursion statement is merely the list of words. "you" is the greatest word (last one alphabetically) in the list. You must return the length to have the previous call level operate on that data.

Please note that this isn't recursion in any but the syntactic sense. Your function has two disparate operations that don't really interact: if it's called with a string, it does one thing; if it's called with any other data type, it iterates. This is not really "base case" and "recursion case", unless you have nested lists of words.

answered Nov 27, 2017 at 22:00

Prune

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Comments

randyr · Accepted Answer · 2017-11-27 22:15:21Z

0

This does not seem like proper use of recursion. It looks more like you're trying to overload the longestWord_with_recursion function with two functionalities:

Change a list of words into a list of tuples with (word_length, word) and
Return the largest word based on the list of tuples.

You could rewrite the entire function into:

def longest_word(iterable):
    return max([(len(x), x) for x in iterable])

which will return the longest word as well, while still using the built-in max function. This will return a tuple of (word_length, word), so if you only want the word returned, you can do:

def longest_word(iterable):
    return max([(len(x), x) for x in iterable])[1]

Notice the [1] at the end.

Edit:

Looking at the documentation of max some more, as well as the comment by @Kenny in the comments, it can be made even simpler with:

def longest_word(iterable):
    return max(iterable, key=len)

At this point, is it really worth being its own function?

edited Nov 27, 2017 at 22:15

answered Nov 27, 2017 at 22:10

randyr

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2 Comments

Kenny Ostrom Over a year ago

See my comment above; you can just tell max to use "key=len" and skip all that.

randyr Over a year ago

Yeah, was just editing that as I saw the docs and your comment.

Pang · Accepted Answer · 2017-11-29 01:36:29Z

0

Try this:

def longestWord_with_recursion(wrds):
if type(wrds) == str:
    return len(wrds),wrds
return max([longestWord_with_recursion(x) for x in wrds])[1]

print(longestWord_with_recursion(words))

It's returning a list of two elements, so you just have to indicate that the element you wanna print is the second one!

edited Nov 29, 2017 at 1:36

Pang

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answered Nov 27, 2017 at 22:04

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