Python Pocket Reference, 3rd Edition

22

|

Python Pocket Reference

Lists

Lists are mutable (changeable) arrays of object references,

accessed by offset.

Literals and creation

Lists are written as comma-separated series of values

enclosed in square brackets.

[]

An empty list.

[0, 1, 2, 3]

A four-item list: indexes 0...3.

alist = ['spam', [42, 3.1415], 1.23, {}]

Nested sublists: alist[1][0] fetches 42.

alist = list('spam')

Creates a list by calling the type constructor with a

sequence.

alist = [x**2 for x in range(9)]

Creates a list by collecting expression results (list com-

prehension).

Operations

Operations include all sequence operations (see Table 3, ear-

lier in this book), plus all mutable sequence operations (see

Table 4, earlier in this book), plus the following list methods.

alist.append(x)

Inserts the single object x at the end of alist, changing

the list in-place.

alist.extend(x)

Inserts each item in any sequence x at the end of alist in-

place (an in-place

+). Similar to alist[len(alist):] =

list(x)

.

Specific Built-in Types

|

23

alist.sort([func [, key [, reverse]]])

Sorts alist in-place in ascending order, or per a passed-

in two-argument comparison function

func (which

returns a negative, zero, or positive number to mean the

first argument is smaller than, equal to, or larger than the

second).

key specifies a function of one argument that is

used ...