02List的使用

Lists

by shashank21j

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When we talk about storing multiple values in a container-like data structure, the first thing that comes to mind is a list.

You can initialize a list as:

arr = list()
# or simply
arr = []

or with a few elements as:

arr = [1,2,3]

Elements can be accessed easily similar to most programming languages:

print arr[0]
# result is 1
print arr[0] + arr[1] + arr[2]
# result is 6

Lists in Python are very versatile. You can add almost anything in a Python list.

In Python, you can create a list of any objects: strings, integers, or even lists. You can even add multiple types in a single list!

Let's look at some of the methods you can use on list.

1.) append(x)

Adds a single element x to the end of a list.

arr.append(9)   
print arr  
# prints [1, 2, 3, 9]

2.) extend(L)

Merges another list L to the end.

arr.extend([10,11])
print arr
# prints [1, 2, 3, 9, 10, 11]

3.) insert(i,x) 
Inserts element x at position i.

arr.insert(3,7)
print arr
# prints [1, 2, 3, 7, 9, 10, 11]

4.) remove(x) 
Removes the first occurrence of element x.

arr.remove(10)  
arr  
# prints [1, 2, 3, 7, 9, 11]

5.) pop() 
Removes the last element of a list. If an argument is passed, that index item is popped out.

temp = arr.pop()
print temp 
# prints 11

6.) index(x) 
Returns the first index of a value in the list. Throws an error if it's not found.

temp = arr.index(3)
print temp
# prints 2

7.) count(x) 
Counts the number of occurrences of an element x.

temp = arr.count(1)
print temp
# prints 1

8.) sort() 
Sorts the list.

arr.sort()
print arr
# [1, 2, 3, 7, 9]

9.) reverse() 
Reverses the list.

arr.reverse()
print arr
# [9, 7, 3, 2, 1]