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Python Python Collections (2016, retired 2019) Slices Slice Functions

Posted by Tiago Ramos
Tiago Ramos
2,380 Points

I tried to remove the odds

Hi,

I'm having trouble in the last function, I'm trying to remove the odds so I can return only the evens in reverse.

At first I tried like this : return no_odds[::-2]

but a mate told me I was returning the odds, so it would be better to remove them. Please somebody help me solve this problem

Thanks a bunch!

slices.py 
def first_4(iterable):
    return iterable[:4]

def first_and_last_4(ite):

    head = ite[:4]
    tail = ite[-4:]

    concat = head + tail
    return concat

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

def reverse_evens(iterable):

    #removing the odds
        # returning a variable with the odds
        odds_remove = return iterable[::2]

        # removing that variable from list
        no_odds = iterable.remove(odds_remove)

    return no_odds[::-1]

2 Answers

Keenan Johnson
Keenan Johnson
13,841 Points
Keenan Johnson
Keenan Johnson
13,841 Points

For the last function what you're aiming to do is to first get all of the elements in even numbered positions, and then reverse that list. In your solution, you want to remove that return statement and starting from the beginning (the 0th element), get every other element. The way you're using to reverse [::-1] will work perfectly here. Hope this helps!

Solution:

def first_4(iterable):
    return iterable[:4]

def first_and_last_4(iterable):
    firstFour = iterable[:4]
    lastFour = iterable[-4:]
    return firstFour + lastFour

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

def reverse_evens(iterable):
    evenIterables = iterable[0:][::2]
    return evenIterables[::-1]
Steven Parker
Steven Parker
229,644 Points
Steven Parker
Steven Parker
229,644 Points

:information_source: FYI: making a slice using "[0:]" doesn't do anything except duplicate the array, which isn't needed if you're going to immediately apply another slice.

Keenan Johnson
Keenan Johnson
13,841 Points
Keenan Johnson
Keenan Johnson
13,841 Points

Good catch on that Steven and thanks!

Tiago Ramos
Tiago Ramos
2,380 Points

Hi Keenan, your explanation was great, I knew I had to define the starting position but I had no ideia how.

Thank you so much :)

Steven Parker
Steven Parker
229,644 Points
Steven Parker
Steven Parker
229,644 Points

You have a few issues:

  • you cant use return in an assignment statement
  • if you give remove a list, it will only remove the entire list if it is a sub-item of the main list
  • instead of trying to remove the odds, why not use a slice to return only the evens?