Computer Science · Ch 9 — Lists
Summary
Summary
- Lists are mutable sequences in Python — the elements of a list can be changed after the list is created.
- The elements of a list are written inside square brackets, separated by commas; they may be of mixed data types (integers, floats, strings, tuples, even other lists).
- A list appearing inside another list is a nested list.
- List indexing works like string indexing and starts at 0. Two-way indexing lets you traverse a list forward (0, 1, 2, …) or backward with negative indices (-1 is the last element). An out-of-range index raises IndexError.
- The
+operator concatenates one list to the end of another, producing a new list; both operands must be lists, and the originals are unchanged unless the result is assigned. - The
*operator repeats a list a specified number of times. - The membership operator
intells whether an element is present in a list;not indoes the opposite. - Slicing (
list[start:stop:step]) extracts a part of a list; missing indices default to the ends, an oversized stop truncates, and[::-1]yields the reversed list. - A list can be traversed with a
forloop (directly over elements, or over indices viarange(len())) or with awhileloop and a counter. - Many list manipulation functions and methods are available, including:
len(),list(),append(),extend(),insert(),count(),index(),remove(),pop(),reverse(),sort(),sorted(),min(),max(),sum(). Rememberindex()/remove()raise ValueError for a missing element,sort()/reverse()work in place, andsorted()returns a new list. - An element inside a nested list is reached with two indices:
list[i][j]. …