The list is python Built in data structure in , It takes the form of a collection of different data in square brackets , Separate... With commas . Lists can be used to store the same data type or different data types .
The list is variable , That's why it's so common , In some cases, however , Variability requires special attention .
This paper introduces 11 about python Important operation of list , Help you master the list better .
1. Three ways to remove elements from a list
（1）del
del According to the index position , Delete an element , You can also set the index range to delete , You can also delete the entire list , no return value
Delete single element
a = [1, 2, 'x', 4, 5] del(a[0]) print(f'a is {a}')
Output
a is [2, 'x', 4, 5]
Range delete element
a = [1, 2, 'x', 4, 5] del (a[0:2]) print(f'a is {a}')
Output
a is ['x', 4, 5]
Delete the entire list
a = [1, 2, 'x', 4, 5] del (a[0:5]) print(f'a is {a}') # Delete the elements of the entire list by index range , An empty list will be output a is [] a = [1, 2, 'x', 4, 5] del (a) print(f'a is {a}') # name 'a' is not defined no return value , Error report, no object found
（2）remove
remove() Function to remove the first match of a value in the list , no return value
Example
a = [1, 2, 'x', 4, 5,] a.remove('x') print(f'a is {a}')
Output
a is [1, 2, 4, 5]
Be careful ： Only the first matching value will be deleted , If there is a duplicate, it will not be deleted
a = [1, 2, 'x', 4, 5,'x'] a.remove('x') print(f'a is {a}')
Output :
a is [1, 2, 4, 5, 'x']
（3）pop
pop() Function to remove an element from the list （ Default last element ）, And returns the value of that element .
Example
a = [1, 2, 'x', 4, 5] b = a.pop() print(f'a is {a}') print(f'b is {b}')
Output
a is [1, 2, 'x', 4] b is 5
We can specify the index value of the deleted element , Cannot exceed the total length of the list .
a = [1, 2, 'x', 4, 5] b = a.pop(0) print(f'a is {a}')
Output
a is [2, 'x', 4, 5]
2. Add list , Expand , Insert
（1）append
append() Function is used to add a new object to the end of the list .
a = [1, 2] a.append(3) print(a)
Output
[1, 2, 3]
It can be any data type , The appended element remains the original structure type in the list
a = [1, 2] b = ['x', 'y', 'z'] a.append(b) print(a)
Output
[1, 2, ['x', 'y', 'z']]
list b Became a list a The third item in , If you want to create a list, it's a,b A combination of elements in a list a =(1, 2, 'x', 'y', 'z'), You need to use extend() Function or "+“.
（2）extend
extend() Function to append multiple values in another sequence at the end of the list at one time （ Extend the original list with the new list ）.
a = [1, 2] b = ['x', 'y', 'z'] a.extend(b) print(a)
Output
[1, 2, 'x', 'y', 'z']
（3）insert
insert() Function is also used to add elements to a list . however , It allows you to specify the index of the new element . for example , We can add a new element at the beginning of the list
a = [1, 2, 3, 4, 5] a.insert(0, 'a') print(a)
Output
['a', 1, 2, 3, 4, 5]
insert() The first parameter in is the index , The second is the inserted object
3. use ”=“ Copy list
We can copy a list and create a new variable .
a = [1, 2, 3] b = a print(b)
however , New variable “ b” It's just pointing to “ a” Pointer to value . therefore ,a Any change in the will change b. Let's add a value to confirm .
a = [1, 2, 3] b = a a.append(4) print(a) print(b)
Output
[1, 2, 3, 4]
[1, 2, 3, 4]
4. Copy the list using the index
We can copy the list by selecting all the indexes of the list .
a = [1, 2, 3] b = a[:] print(b)
New list b Include and a The same value , But in different memory locations . If we change a,b Not affected .
a = [1, 2, 3] b = a[:] a.append(4) print(a) print(b)
Output
[1, 2, 3, 4]
[1, 2, 3]
Use copy() Function copy list works the same way as index replication .
a = [1, 2, 3] b = a.copy() a.append(4) print(a) print(b)
Output
[1, 2, 3, 4]
[1, 2, 3]
5. use sort() and sorted() Sort list .
sort and sorted Function can be used to sort a list .
- sort()： Sort list , But it doesn't return anything .
- sorted()： Returns a sorted copy of the list , But don't sort the original list .
sort()
a = [2, 0, 4, 3] b = a.sort() print(a) print(b)
Output
[0, 2, 3, 4]
None
use sorted() Function does the same thing .
a = [2, 0, 4, 3] b = sorted(a) print(a) print(b)
Output
[2, 0, 4, 3]
[0, 2, 3, 4]
6. Create nested lists by copying
When creating a nested list by copying , We need to pay attention to the changes in the elements . Any modification of the original list element changes the copied list .
a = [1, 2] b = ['x', 'y'] c = [a, b] a.append(3) b.pop() print(a) print(b) print(c)
list c By list a And list b form , We updated the list by adding and removing an element a And list b. therefore , list c Also updated .
Output
[1, 2, 3] ['x'] [[1, 2, 3], ['x']]
To be continued ...
