There are also two directions to move through the list (from first to last element and from last to first element). Beginning/end can also be thought of as top/bottom or front/back. There are two ends to the list: the beginning where index=0 (the first element) and the end where index=highest value (the last element). Second note, when no start is defined as in A, it defaults to 0. Therefore, the elements before the stop sign are returned. is putting the stop sign at index 2, which is the third element. You stop before the stop sign, not at it or after it. First note, although we indexed with 0:2 which expands out to, only 2 elements are returned. Exercise 1: Retrieve the first two elements from List A Solution print("The first two elements of A:",A, A)
Slice back of list code#
If you are having trouble, you can see the solution below the exercise.įor all of these exercises, write your code in the box provided under the exercise description and click “Run” to test the output. Given the pattern aList, retrieve the first two elements from List A. To retrieve a subset of elements, the start and stop positions need to be defined. For example, all values are retrieved with a colon. With extended indexing syntax, we retrieve a range of values. List A’s elements are numbered according to the ordinal position (the first element is 1, the second element is 2, etc) while List B’s elements are the numbers that would be used to index them ( for the first element 0, etc). This is why we are using 2 lists for this exercise. It is important to note, the first element is index 0, NOT index 1. Since the start defaults to none, this translates into retrieving only one element. Python 3.4 documentationĪs you can see, defining only stop returns one element. Did you notice this is similar to how range was used to define lists A and B? This is because the slice object represents the set of indices specified by range(start, stop, step).
The start argument and the step argument both default to none – the only required argument is stop. # Index the number 3 from A and the number 6 from B.Įxtended indexing syntax used for slicing is aList. # The second is also a numeric list, from 0 to 9 (List B)Ī = list(range(1,10,1)) # start,stop,step # Create two lists to slice, the first is a numeric list from 1 to 9 (List A). We will review the basic way to retrieve data from a list, as well as some more advanced techniques.įirst, we will create a list of values to use in our slicing.
Slice back of list trial#
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