Effective List Management in Python Programming
Learn how to efficiently store and manipulate multiple pieces of data using lists in Python. Explore techniques such as adding to a list, editing list contents, and removing items by index or value. Discover the power of lists for handling large sets of data effortlessly.
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Presentation Transcript
Lists CMSC 201
Motivation If we want to average three numbers, we can easily do the following: num1 = input( Please enter a number: ) num2 = input( Please enter a number: ) num3 = input( Please enter a number: ) print((num1 + num2 + num3) / 3) What if we want to average a 100 different numbers? Do we make a 100 different variables?
Lists Lists are a way of storing multiple pieces of information in the same place! They work like this: myList = [9, 10, 11] Creates three variables, one that has the value 9, one with the value 10, and one with the value 11. These are stored in order! print(myList[0]) Prints 9, since it is the first thing in the list. myList[1] will be 10, and myList[2] will be 11.
Lists Why is this better? This means that we can refer to items in the list by their number (or index index). The index can be a variable or an actual number. a = 10 print(myList[a]) Also, the lists can get as big as we want!
Adding to a List If you want to add something to the end of a list, simply call append. myList = [ 3, 4, 5] myList.append(6) print(myList) (3, 4, 5, 6)
Editing List Contents If you want to change something in a list, just use the assignment operator! myList = [1, 2, 3] myList[1] = 100 print(myList) (1, 100, 3)
Remove By Index If you want to delete something at a certain index, just call pop(index). myList = [10, 12, 14] myList.pop(1) print(myList) (10, 14)
Remove By Value If you want to delete a certain value from a list, use remove(value) myList = [10, 12, 14] myList.remove(14) print(myList) (10, 12)
List Contents Lists can hold any combination of types! This is fine: myList = [ hi , True, 10] We can even put lists inside lists! myList = [ [1, 2, 3], [4, 5, 6], [7, 8, 9]]
2D Lists myList = [ [1, 2, 3], [4, 5, 6], [7, 8, 9]] When thinking of 2D lists, think of it as a grid! 1 2 3 4 5 6 7 8 9 If you want to get out the thing at row 1, col 2 you write: myList[1][2]
