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Python

Posted by ASHOK Gudivada
ASHOK Gudivada
11,701 Points

reverse_evens

You're on fire! Last one and it is, of course, the hardest. Make a function named reverse_evens that accepts a single iterable as an argument. Return every item in the iterable with an even index...in reverse. For example, with [1, 2, 3, 4, 5] as the input, the function would return [5, 3, 1]. You can do it!

Can someone help with reverse Challenge Task 4 of 4. Its not passing

def first_4(list_items):
    return (list_items[0:4])

def first_and_last_4(item):
    return item[:4] + item[-4::1]

def odds(item):
    return item[1::2]

def reverse_evens(item):
    item.reverse()
    return (item[::2])
ASHOK Gudivada
ASHOK Gudivada
11,701 Points 
>>> item
[1, 2, 3, 4, 5]
>>> i= list(item[0::2])
>>> i
[1, 3, 5]
>>> item = [1, 2, 3, 4, 5]
>>> item.reverse()
>>> item[::2]
[5, 3, 1]

It work on my computer

3 Answers

Steven Fitzpatrick
Steven Fitzpatrick
4,022 Points

Slice Notation

print(agr4[::-2])
Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,468 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,468 Points

What happens when you have an even number of items?

>>> item = [1, 2, 3, 4, 5, 6]
>>> item.reverse()
>>> item
[6, 5, 4, 3, 2, 1]
>>> item[::2]
[6, 4, 2]

It gives the "even items of the reverse" but it should be the "reverse of the even items".

Hint: Try getting the even indexed items first, then reverse the result.

ASHOK Gudivada
ASHOK Gudivada
11,701 Points 
def reverse_evens(agr4):
    i = list(agr4[::2])
    return (i.reverse())

Still it is not passing.

>>> agr4 = [1, 2, 3, 4, 5,6]
>>> i = list(agr4[::2]).reverse()
>>> i
>>> agr4
[1, 2, 3, 4, 5, 6]
>>> i = list(agr4[::2])
>>> i
[1, 3, 5]
>>> i.reverse()
>>> i
[5, 3, 1]

https://teamtreehouse.com/library/python-collections-2/slices/slice-functions

Chris Freeman
Chris Freeman
Treehouse Moderator 68,468 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,468 Points

Instead of reverse(), try using slice notation to reverse the list: [::-1]

Chris Freeman
Chris Freeman
Treehouse Moderator 68,468 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,468 Points

reverse() method modifies a list in place. Its return value is None. So, the statement:

return (i.reverse())

returns None

ASHOK Gudivada
ASHOK Gudivada
11,701 Points
ASHOK Gudivada
ASHOK Gudivada
11,701 Points

Thank you Chris Freeman it worked out