Python căn bản (13): Python Lists

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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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