List slicing (selecting parts of lists) is useful in performing different tasks and getting desired outputs. Learn more about Python List slicing here.
Python List slicing: Using the third “step” argument
lst = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h']
lst[::2]
Output: [‘a’, ‘c’, ‘e’, ‘g’]
lst[::3]
Output: [‘a’, ‘d’, ‘g’]
Section 22.2: Selecting a sublist from a list
lst = ['a', 'b', 'c', 'd', 'e']
lst[2:4]
Output: [‘c’, ‘d’]
lst[2:]
Output: [‘c’, ‘d’, ‘e’]
lst[:4]
Output: [‘a’, ‘b’, ‘c’, ‘d’]
Python List slicing: Reversing a list with slicing
a = [1, 2, 3, 4, 5]
steps through the list backwards (step=-1) b = a[::-1]
built-in list method to reverse 'a' a.reverse()
if a = b:
print(True)
print(b)
Output:
True
[5, 4, 3, 2, 1]
Python List slicing: Shifting a list using slicing
def shift_list(array, s):
"""Shifts the elements of a list to the left or right.
Args:
array - the list to shift
s - the amount to shift the list ('+': right-shift, '-': left-shift)
Returns:
shifted_array - the shifted list
“””
calculate actual shift amount (e.g., 11 --> 1 if length of the array is 5) s %= len(array)
reverse the shift direction to be more intuitive
s *= -1
shift array with list slicing shifted_array = array[s:] + array[:s]
return shifted_array
my_array = [1, 2, 3, 4, 5]
negative numbers
shift_list(my_array, -7)
[3, 4, 5, 1, 2]
no shift on numbers equal to the size of the array shift_list(my_array, 5)
[1, 2, 3, 4, 5]
works on positive numbers
shift_list(my_array, 3)
[3, 4, 5, 1, 2]
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