Python: List Basics
List Basics
Creating List
[item_0, item_1, item_2, …]
# -*- coding: utf-8 -*- # python a = [0, 1, 2, "m", 4, 5] print a # [0, 1, 2, 'm', 4, 5]
Count Elements
len(list)
# -*- coding: utf-8 -*- # python # Get length a = ["more", 4, 6] print len(a) # prints 3
Get a Element
List element can be extracted with the form list[index].
# -*- coding: utf-8 -*- # python # get one element a = ["more", 4, 6] print a[1] # prints 4
Negative index counts from right.
# -*- coding: utf-8 -*- # python a = ["more", 4, 6] print a[-1] # prints 6 # negative index counts from right
Change a Element
A element can be changed with the form list[index] = new_value.
# -*- coding: utf-8 -*- # python a = ["zero", "one", "two"] a[2] = "b" print a # prints ['zero', 'one', 'b']
Delete a Element
Use the “del” statement: del list[index].
# -*- coding: utf-8 -*- # python a = ["zero","one","two","three"] del a[2] print a # ['zero', 'one', 'three']
Get Sublist
Sublist can be extracted using the form list[start_index:end_index]. (warning: end_index element is not included. For example, mylist[1:2] returns only 1 elements, not 2.)
# -*- coding: utf-8 -*- # python a = ["zero", "one", "two", "three", "four", "five"] print a[1:4] # ⇒ ['one', 'two', 'three'] # if first index is ommited, default to 0 print a[:4] # ⇒ ['zero', 'one', 'two', 'three'] # if second index is ommited, default length of list. Effectively, up to last element print a[0:] # ⇒ ['zero', 'one', 'two', 'three', 'four', 'five'] # get everything print a[:] # ⇒ ['zero', 'one', 'two', 'three', 'four', 'five'] # negative counts from last. Not include last. print a[0:-1] # ⇒ ['zero', 'one', 'two', 'three', 'four']
Change Sublist
A slice (sublist) of elements can be changed by assigning to a list directly. The length of the slice need not match the length of new list.
list[index1:index2] = new_list → replace a sublist by new_list.
# -*- coding: utf-8 -*- # python a = [0, 1, 2, 3, 4, 5] a[2:4] = ["a", "b"] print a # [0, 1, 'a', 'b', 4, 5]
Nested Lists
Lists can be nested arbitrarily. Append extra bracket to get element of nested list.
# -*- coding: utf-8 -*- # python a = [3, 4, [7, 8]] print a print a[2][1] # returns 8
Join 2 Lists
Lists can be joined with plus sign.
# -*- coding: utf-8 -*- # python b = ["a", "b"] + [7, 6] print b # prints ['a', 'b', 7, 6]
5. Built-in Types — Python v2.7.6 documentation #mutable-sequence-types