Lists, Indexing, and Slicing (Python Basics 4)

Powerful Data Types

  • lists and dictionaries are both powerful data types
  • learning to use them well can greatly enhance what you can do with Python

Creating a List

  • a list is simply a collection of items inside square brackets:

mylist = ['a','b','c','d']

  • you can mix the data types of things in the list

mixedlist = [1,2,'a','ryan']

  • you can also create a list of integers using the range function:

intlist = range(10)

Indexing

  • grabbing one element out of a list is done with square brackets and an integer index:
mylist = ['a','b','c','d']
item1 = mylist[1]
  • what will item1 be?
    • try it out now

Parentheses vs. Square Brackets

  • note that Python uses parentheses for calling functions and square brackets for indexing and slicing of lists:
myfunc(a,b)
myitem = mylist[2]

Negative Indices

  • negative indices also work on lists
  • mylist[-1] refers to the last item in the list
    • mylist[-2] would refer to the second to the last item and so on

Slicing

  • slicing refers to extracting a sublist from a list using a start and stop index seperated by a colon:
mylist = ['a','b','c','d']
myslice = mylist[0:2]
  • note that like range(2), the slice stopping index is one less than the second number
    • try out the code above
    • what is myslice?