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

Albert Tomasura
Albert Tomasura
11,041 Points
Posted by Albert Tomasura
Albert Tomasura
11,041 Points

Slice Functions

For this challenge I completed 3 out 4 steps with ease. I started running into constant errors/incorrect values messages with the last portion (reverse_evens). I ran the same code through Workspaces with no errors and when I adjusted the code to print instead of return, using the example provided ([1, 2, 3, 4, 5]). The result was [5, 3, 1] which was the intended answer according to the example.

slices.py 
def first_4(ok):
    return ok[0:4]

def first_and_last_4(ok):
    return ok[0:4] + ok[-4:]

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

def reverse_evens(ok):
    return ok[-1::-2]

2 Answers

james south
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
james south
Front End Web Development Techdegree Graduate 33,271 Points
james south
.a{fill-rule:evenodd;}techdegree seal-36
james south
Front End Web Development Techdegree Graduate 33,271 Points

[::-2] works fine if the list length is odd. if the length is even, then the last index is odd, and you will get every odd index. so you either need to test for length and cut off the last element if it has an odd index (to use [::-2]), or slice out the evens from the beginning of the list (from index 0), then reverse.

Albert Tomasura
Albert Tomasura
11,041 Points
Albert Tomasura
Albert Tomasura
11,041 Points

Thanks for your help James. This is what my resulting code.

def first_4(ok):

return ok[0:4]

def first_and_last_4(ok):

return ok[0:4] + ok[-4:]

def odds(ok):

return ok[1::2]

def reverse_evens(ok):

if len(ok) % 2:
    return ok[-1::-2]

else:
    del ok[-1]
    return ok[-1::-2]
Nemanja Savkic
Nemanja Savkic
17,418 Points
Nemanja Savkic
Nemanja Savkic
17,418 Points

I tried the following code in repl and workspaces

def reverse_evens(word):
    reverse = word[::-1]
    return reverse[::2]

and I got the expected result [5, 3, 1] but it wasn't accepted. Any idea why?

I finished the task by slicing the evens out and then reversing, like James suggested