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Python Python Collections (Retired) Slices Slice Functions

Abe Daniels
PLUS
Abe Daniels
Courses Plus Student 2,781 Points
Posted by Abe Daniels
Abe Daniels
Courses Plus Student 2,781 Points

I am so close.. need help slicing.

I am getting [1,2,3,4,5,49,48,47,46,45] should be getting [1,2,3,4,5,45,46,47,48,49]

I want to be able to solve this with the ability to insert any iterable into var, to make it universal. (Works for 1-100, and 1,-50)

Thanks! :)

slices.py 
question = "Make a function name first_and_last_4 that accepts an iterable and returns the first 4 and last 4 items in the iterable."
var = []
def first_4(var):
  return var[:4]
def odds(var):
  return var[1::2]
def first_and_last_4(var):
  solution =  var[:4] + var[:-5:-1]
  return solution

2 Answers

Tatiana Jamison
Tatiana Jamison
6,188 Points
Tatiana Jamison
Tatiana Jamison
6,188 Points

Since you've passed -1 as the step size, it's traversing the list backwards. You want to traverse the list forward (i.e., with the default step size of "1"), just modify the starting position.

Tatiana Jamison
Tatiana Jamison
6,188 Points

In case this is overly cryptic, remember that when you do something like 

var[:-5:-1]

... the syntax is 

iterable[start:end:stepsize]

So it says, "count backward by 1 from the end of var until you reach the element whose index is 5 less than the length of the list."

Christian Lapinig
Christian Lapinig
6,396 Points
Christian Lapinig
Christian Lapinig
6,396 Points

You can do something like var[8:] (I know it's supposed to be 4, but you get the picture), it's like you are going backwards in the list much like how var[:8] goes forward in the list and slicing it at how many items you want. You can also simplify the function by doing:

def first_and_last_4(var): return ......