Bài trước: Python căn bản (12): Python Loops
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13. Python Lists
13.1 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.
Example
Create a List:
thislist = ["apple", "banana", "cherry"]
print(thislist)
List Items
List items are ordered, changeable, and allow duplicate values.
List items are indexed, the first item has index [0], the second item has index [1] etc.
Example:
print(thislist[0])
# print out: apple
Ordered
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.
Note: There are some list methods that will change the order, but in general: the order of the items will not change.
Changeable
The list is changeable, meaning that we can change, add, and remove items in a list after it has been created.
Allow Duplicates
Since lists are indexed, lists can have items with the same value.
Example
Lists allow duplicate values:
thislist = ["apple", "banana", "cherry", "apple", "cherry"]
print(thislist)
List Length
To determine how many items a list has, use the len() function.
Example
Print the number of items in the list:
thislist = ["apple", "banana", "cherry"]
print(len(thislist))
List Items - Data Types
List items can be of any data type.
Example
String, int and boolean data types:
list1 = ["apple", "banana", "cherry"]
list2 = [1, 5, 7, 9, 3]
list3 = [True, False, False]
A list can contain different data types.
Example
A list with strings, integers and boolean values:
list1 = ["abc", 34, True, 40, "male"]
type()
From Python's perspective, lists are defined as objects with the data type 'list'.
<class 'list'>
Example
What is the data type of a list?
mylist = ["apple", "banana", "cherry"]
print(type(mylist))
The list() Constructor
It is also possible to use the list() constructor when creating a new list.
Example
Using the list() constructor to make a List:
thislist = list(("apple", "banana", "cherry")) # note the double round-brackets
print(thislist)
Python Collections (Arrays)
There are four collection data types in the Python programming language:
List is a collection which is ordered and changeable. Allows duplicate members.
Tuple is a collection which is ordered and unchangeable. Allows duplicate members.
Set is a collection which is unordered, unchangeable*, and unindexed. No duplicate members.
Dictionary is a collection which is ordered** and changeable. No duplicate members.
*Set items are unchangeable, but you can remove and/or add items whenever you like.
**As of Python version 3.7, dictionaries are ordered. In Python 3.6 and earlier, dictionaries are
unordered.
When choosing a collection type, it is useful to understand the properties of that type. Choosing the right type for a particular data set could mean retention of meaning, and it could mean an increase in efficiency or security.
13.2 Exercise
1. What will be the result of the following code:
mylist = ['apple', 'banana', 'cherry']
print(mylist[1])
A. apple
B. banana
C. cherry
D. mylist
2. What will be the result of the following code:
mylist = ['apple', 'banana', 'cherry']
print(len(mylist))
A. 2
B. 4
C. 3
D. 1
3. Write a Python program to create a list to store student’s
information, including: name, age, gender, GPA. Print out the student’s
information following this pattern:
Information of Student:
['Teo', 16, 'male', 3.0]
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The answer hints:
1(B), 2(C)
3. Write a Python program to create a list to store student’s
information, including: name, age, gender, GPA. Print out the student’s
information following this pattern:
Information of Student:
['Teo', 16, 'male', 3.0]
[code13_3.py]
# Create a list to store student
information
studentInfo = ["Teo", 16,
"male", 3.0]
# Print the student's information
print("Information of
Student:")
print(studentInfo)
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Cập nhật: 31/10/2024
Bài sau: Python căn bản (14):
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