List Slicing Part 2
Part of the Fundamentals section of Coddy's Python journey — lesson 65 of 77.
Slicing has another step parameter: lst[start:stop:step], For example consider this list:
numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]Gets every second element from index 1 to 8:
print(numbers[1:8:2])
# Output: [1, 3, 5, 7]Gets every third element from index 2:
print(numbers[2::3])
# Output: [2, 5, 8]Slicing also supports negative indices.
Counting from end:
print(numbers[-3:])
# Output: [7, 8, 9]Here, -3 means "start 3 positions from the end"
Count until end:
print(numbers[:-2])
# Output: [0, 1, 2, 3, 4, 5, 6, 7]Here, -2 means "stop 2 positions from the end" (exclusive)
Reversing with negative step:
print(numbers[::-1])
# Output: [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]- Empty space before first
:means “start from beginning” - Empty space between
:means “go until the end” - -1 means "move backwards one step at a time"
Challenge
EasyCreate a program that receives a list as input (given) and prints three new lists based on the following slicing operations:
- A list containing every third element, starting from index 1 (the second element)
- A list containing all the elements from the 6th element to the 1st in reverse order
- A list containing every second element starting from the middle of the list to the end
Cheat sheet
Slicing syntax: lst[start:stop:step]
Examples of slicing:
numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
# Every second element from index 1 to 8
print(numbers[1:8:2]) # Output: [1, 3, 5, 7]
# Every third element from index 2
print(numbers[2::3]) # Output: [2, 5, 8]
# Last three elements
print(numbers[-3:]) # Output: [7, 8, 9]
# All elements except last two
print(numbers[:-2]) # Output: [0, 1, 2, 3, 4, 5, 6, 7]
# Reverse the list
print(numbers[::-1]) # Output: [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]Key points:
- Negative indices count from the end of the list
- Empty space before first
:means "start from beginning" - Empty space between
:means "go until the end" - Negative step reverses the order
Try it yourself
lst = input().split(",")
# Write your code below
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
All lessons in Fundamentals
4Operators Part 2
Logical Operators Part 1Logical Operators Part 2Recap - Simple LogicLogical Operators Part 3Logical Operators Part 4
8Loops
For LoopWhile LoopBreakContinueRecap - FactorialThe Range FunctionNested LoopRecap - Dynamic Input3Operators Part 1
Arithmetic OperatorsModulo OperatorArithmetic ShortcutsRecap - Simple MathComparison Operators9Functions
Declare a FunctionArgumentsReturnRecap - Sigma FunctionRecap - Validation FunctionDefault Values12Iterating Over Sequences
Iterating Over ElementsThe Enumerate FunctionIterating Over Strings Part 1Iterating Over Strings Part 2