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

jmac pd
jmac pd
11,490 Points
Posted by jmac pd
jmac pd
11,490 Points

hmm, am I reading this one wrong? I ran the function through the shell and it returns [5,3,1]

question says to count down "even" in reverse so that list [1, 2, 3, 4, 5] would return as [5, 3, 1] (though this seems like reverse odds, the question was not completed when I ran the function with a [-2: :-2]slice/step returning [4, 2])

slices.py 
def first_4(item):
    item = list(item)
    return item[0:4]

def first_and_last_4(item):
    first = first_4(item)
    item = list(item)
    return first + item[-4:]

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

def reverse_evens(item):
    item = list(item)
    return item[::-2]
Igor Ević
Igor Ević
5,827 Points

You don't need item = list(item) because slice works on every iterable.

item[::-2] returns [5, 3, 1] for list [1, 2, 3, 4, 5], but what if list is [1, 2, 3, 4, 5, 6]?

jmac pd
jmac pd
11,490 Points
jmac pd
jmac pd
11,490 Points

ok I got it. thanks Igor:

I added an if/else clause to determine if the length of the iterable was even and then added a variable to the slice:

'''python3

def reverse_evens(item): if len(item)%2==0: slice = -2 else: slice = -1 return item[slice::-2] '''

Igor Ević
Igor Ević
5,827 Points

jmac pd, you don't need to know if the length of iterable is even or odd:

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