list
Lists are used to store multiple items in a single variable.
Lists are one of 4 built-in data types in Python used to store collections of data, the other 3 are Tuple, Set, and Dictionary, all with different qualities and usage.
Lists are created using square brackets:
mylist = ["apple", "banana", "cherry"]
print(mylist)
List items are ordered, changeable, and allow duplicate values(Since lists are indexed, lists can have items with the same value).
List items are indexed, the first item has index [0], the second item has index [1] etc.
When we say that lists are ordered, it means that the items have a defined order, and that order will not change.
If you add new items to a list, the new items will be placed at the end of the list.
thislist = ["apple", "banana", "cherry", "apple", "cherry"]
print(thislist)
print(len(thislist)) # length of list
A list can contain different data types:
list1 = ["abc", 34, True, 40, "male"]
type()
mylist = ["apple", "banana", "cherry"]
print(type(mylist))
<class 'list'>
constructor
thislist = list(("apple", "banana", "cherry")) # note the double round-brackets
print(thislist)
access
thislist = ["apple", "banana", "cherry"]
print(thislist[-1])
print(thislist[1])
fruits = ["apple", "banana", "cherry", "orange", "kiwi", "melon", "mango"]
print(fruits[2:5])
print(fruits[-4:-1])
if "apple" in thislist:
print("Yes, 'apple' is in the fruits list")
cherry
banana
['cherry', 'orange', 'kiwi']
['orange', 'kiwi', 'melon']
Yes, 'apple' is in the fruits list
change
thislist = ["apple", "banana", "cherry", "orange", "kiwi", "mango"]
thislist[1:3] = ["blackcurrant", "watermelon"]
print(thislist)
thislist = ["apple", "banana", "cherry"]
thislist[1:2] = ["blackcurrant", "watermelon"]
print(thislist)
thislist = ["apple", "banana", "cherry"]
thislist[1:3] = ["blackcurrant"]
print(thislist)
['apple', 'blackcurrant', 'watermelon', 'orange', 'kiwi','mango']
['apple', 'blackcurrant', 'watermelon', 'cherry']
['apple',"blackcurrant"]
insert & remove
ls2 = ["mango", "pineapple", "papaya"]
ls = ["apple", "banana", "cherry"]
ls.append("orange")
print(ls)
ls.insert(1,"melon")
print(ls)
ls.extend(ls2)
print(ls)
ls.append("banana")
ls.remove("banana")
print(ls)
ls.pop(1)
print(ls)
ls.pop()
print(ls)
ls.clear()
print(ls)
del ls
print(ls)
["apple","banana","cherry", "orange"]
["apple","melon","banana","cherry", "orange"]
["apple","melon","banana","cherry", "orange","mango","pineapple","papaya"]
["apple","melon","cherry", "orange","mango","pineapple","papaya","banana"]
["apple","cherry", "orange","mango","pineapple","papaya","banana"]
["apple","cherry", "orange","mango","pineapple","papaya"]
[]
NameError: name 'thislist' is not defined
If you do not specify the index, the pop() method removes the last item.
If there are more than one item with the specified value, the remove() method removes the first occurance;
The extend() method does not have to append lists, you can add any iterable object (tuples, sets, dictionaries etc.).
thislist = ["apple", "banana", "cherry"]
thistuple = ("kiwi", "orange")
thislist.extend(thistuple)
print(thislist)
loop
thislist = ["apple", "banana", "cherry"]
for x in thislist:
print(x)
for i in range(len(thislist)):
print(thislist[i]) # The iterable created in the example above is [0, 1, 2].
thislist = ["apple", "banana", "cherry"]
i = 0
while i < len(thislist):
print(thislist[i])
i = i + 1
list comprehension
newlist = [expression for item in iterable if condition == True]
list comprehension offers the shortest syntax for looping through lists:
thislist = ["apple", "banana", "cherry"]
[print(x) for x in thislist]
apple
banana
cherry
fruits = ["apple", "banana", "cherry", "kiwi", "mango"]
newlist = [x for x in fruits if "a" in x]
print(newlist)
newlist = [x for x in range(10)]
newlist = [x.upper() for x in fruits]
newlist = ['hello' for x in fruits] # 将所有的fruits的都换成hello
newlist = [x if x != "banana" else "orange" for x in fruits] # 如果不是banana就是x，将所有的banana换成orange
['apple', 'banana', 'mango']
sort
List objects have a sort() method that will sort the list alphanumerically, ascending, by default:
foods = ["orange", "mango", "kiwi", "pineapple", "banana"]
foods.sort()
print(foods)
nums = [100, 50, 65, 82, 23]
nums.sort()
print(nums)
nums.sort(reverse=true)
print(nums)
["banana","kiwi","mango","orange","pineapple"]
[23,50,65,82,100]
[100,82,65,50,23]
By default the sort() method is case sensitive, resulting in all capital letters being sorted before lower case letters: 大小写敏感，大写在小写前面
thislist.sort(key = str.lower)
You can also customize your own function by using the keyword argument key = function.
The function will return a number that will be used to sort the list (the lowest number first):
# Sort the list based on how close the number is to 50:
def myfunc(n):
return abs(n - 50)
thislist = [100, 50, 65, 82, 23]
thislist.sort(key = myfunc)
print(thislist)
thislist = ["banana", "Orange", "Kiwi", "cherry"]
thislist.reverse()
print(thislist)
copy()
You cannot copy a list simply by typing list2 = list1, because: list2 will only be a reference to list1, and changes made in list1 will automatically also be made in list2.
There are ways to make a copy, one way is to use the built-in List method copy().
thislist = ["apple", "banana", "cherry"]
mylist = thislist.copy()
print(mylist)
Another way to make a copy is to use the built-in method list().
thislist = ["apple", "banana", "cherry"]
mylist = list(thislist)
print(mylist)
join
list1 = ["a", "b", "c"]
list2 = [1, 2, 3]
list3 = list1 + list2
print(list3)
["a","b","c",1,2,3]
成员函数
| name | description |
|---|---|
| append() | Adds an element at the end of the list |
| clear() | Removes all the elements from the list |
| copy() | Returns a copy of the list |
| count() | Returns the number of elements with the specified value |
| extend() | Add the elements of a list (or any iterable), to the end of the current list |
| index() | Returns the index of the first element with the specified value |
| insert() | Adds an element at the specified position |
| pop() | Removes the element at the specified position |
| remove() | Removes the item with the specified value |
| reverse() | Reverses the order of the list |
| sort() | Sorts the list |