Square brackets let you create lists and access particular parts of sequences. Put an integer index inside the brackets to retrieve one item or character; use a colon-based slice to retrieve a group of characters. section 25.2 section 7.2
Reading a grocery list
grocery = ["milk", "eggs", "bread"] print(grocery[0]) print(grocery[1]) print(grocery[2]) Python starts counting at 0, so these lines print milk, eggs, and bread. The list has three elements, and index 3 is beyond its limits. section 25.2
Remember these rules:
- The first element or character is at index 0. section 25.2 section 7.2
- Negative indexes count backward; the last character in a string is at index -1. section 7.2
- A slice uses the form [start_index:stop_index:step] to extract part of a string. section 7.2
- An invalid list index raises an IndexError because it is outside the list. section 25.2
Figure 7.1. The string “Python rules!” and the index of each character. The first row shows indexing with positive integers, and the second row shows indexing with negative integers.
Use the character-index diagram to see positive and negative positions arranged around the string “Python rules!”. section 7.2
