1. Format of Lists
A list is an ordered collection that allows you to add and remove elements at any time.
Each element in a list is assigned a number – its position, or index, with the first index being 0, the second index being 1, and so on.
list1 = ['physics', 'chemistry', 1997, 2000]list2 = [1, 2, 3, 4, 5 ]list3 = ["a", "b", "c", "d"]
print("list1[0]: {}".format(list1[0])) # Access
print("list2[1:5]: {}".format(list2[1:5])) # Slice
print("list3: {}".format(list3.append("e"))) # Use append() to add an elementThe output of the above example is:
list1[0]: physicslist2[1:5]: [2, 3, 4, 5]list3: ["a", "b", "c", "d", "e"]2. List Operators
The operators + and * for lists are similar to those for strings. The + operator is used to concatenate lists, while the * operator is used to repeat lists.
As shown below:
|
Python Expression |
Result |
Description |
|
len([1, 2, 3]) |
3 |
Count of elements |
|
[1, 2, 3] + [4, 5, 6] |
[1, 2, 3, 4, 5, 6] |
Concatenation |
|
[‘Hi!’] * 4 |
[‘Hi!’, ‘Hi!’, ‘Hi!’, ‘Hi!’] |
Replication |
|
3 in [1, 2, 3] |
True |
Check if an element exists in the list |
|
[1, 2, 3, 4, 5, 6][:3] |
[1,2,3] |
Slicing |
|
for x in [1, 2, 3]: print x, |
1 2 3 |
Iteration |
3. Common List Operations
Common methods:
|
Method |
Description |
|
len(list) |
Count of list elements |
|
max(list) |
Return the maximum value in the list |
|
min(list) |
Return the minimum value in the list |
|
list(seq) |
Convert a tuple to a list |
|
list.append(obj) |
Add a new object to the end of the list |
|
list.count(obj) |
Count occurrences of an element in the list |
|
list.extend(seq) |
Add multiple values from another sequence to the end of the list (extend the original list) |
|
list.index(obj) |
Find the index of the first occurrence of a value in the list |
|
list.insert(index, obj) |
Insert an object into the list |
|
list.pop([index=-1]) |
Remove an element from the list (default is the last element) and return its value |
|
list.remove(obj) |
Remove the first occurrence of a value from the list |
|
list.reverse() |
Reverse the elements in the list |
|
list.sort(cmp=None, key=None, reverse=False) |
Sort the original list |
4. Traversing Lists
#!/usr/bin/env python
# -*- coding: utf-8 -*-
if __name__ == '__main__': list = ['html', 'js', 'css', 'python']
# Method 1 print 'Traversing list method 1:' for i in list: print ("Index: %s Value: %s" % (list.index(i) + 1, i))
print '
Traversing list method 2:'
# Method 2 for i in range(len(list)): print ("Index: %s Value: %s" % (i + 1, list[i]))
# Method 3 print '
Traversing list method 3:' for i, val in enumerate(list): print ("Index: %s Value: %s" % (i + 1, val))
# Method 3 print '
Traversing list method 3 (setting initial position, only changing the starting index):' for i, val in enumerate(list, 2): print ("Index: %s Value: %s" % (i + 1, val))