Python căn bản (14): Python Lists (cont.1)

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14. Python Lists (cont.1)

14.1 Access List Items

Access Items

List items are indexed and you can access them by referring to the index number.

Example

Print the second item of the list.

thislist = ["apple", "banana", "cherry"]

print(thislist[1])

Note: The first item has index 0.

Negative Indexing

Negative indexing means start from the end

-1 refers to the last item, -2 refers to the second last item etc.

Example

Print the last item of the list:

thislist = ["apple", "banana", "cherry"]

print(thislist[-1])

Range of Indexes

You can specify a range of indexes by specifying where to start and where to end the range.

When specifying a range, the return value will be a new list with the specified items.

Example

Return the third, fourth, and fifth item:

thislist = ["apple", "banana", "cherry", "orange", "kiwi", "melon", "mango"]

print(thislist[2:5])

Note: The search will start at index 2 (included) and end at index 5 (not included).

Remember that the first item has index 0.

By leaving out the start value, the range will start at the first item:

Example

This example returns the items from the beginning to, but NOT including, "kiwi":

thislist = ["apple", "banana", "cherry", "orange", "kiwi", "melon", "mango"]

print(thislist[:4])

By leaving out the end value, the range will go on to the end of the list:

Example

This example returns the items from "cherry" to the end:

thislist = ["apple", "banana", "cherry", "orange", "kiwi", "melon", "mango"]

print(thislist[2:])

Range of Negative Indexes

Specify negative indexes if you want to start the search from the end of the list.

Example

This example returns the items from "orange" (-4) to, but NOT including "mango" (-1):

thislist = ["apple", "banana", "cherry", "orange", "kiwi", "melon", "mango"]

print(thislist[-4:-1])

Check if Item Exists

To determine if a specified item is present in a list use the in keyword.

Example

Check if "apple" is present in the list:

thislist = ["apple", "banana", "cherry"]

if "apple" in thislist:

  print("Yes, 'apple' is in the fruits list")

14.2 Change Item Value

To change the value of a specific item, refer to the index number.

Example

Change the second item:

thislist = ["apple", "banana", "cherry"]

thislist[1] = "blackcurrant"

print(thislist)

Change a Range of Item Values

To change the value of items within a specific range, define a list with the new values, and refer to the range of index numbers where you want to insert the new values.

Example

Change the values "banana" and "cherry" with the values "blackcurrant" and "watermelon":

thislist = ["apple", "banana", "cherry", "orange", "kiwi", "mango"]

thislist[1:3] = ["blackcurrant", "watermelon"]

print(thislist)

If you insert more items than you replace, the new items will be inserted where you specified, and the remaining items will move accordingly.

Example

Change the second value by replacing it with two new values:

thislist = ["apple", "banana", "cherry"]

thislist[1:2] = ["blackcurrant", "watermelon"]

print(thislist)

Note: The length of the list will change when the number of items inserted does not match the number of items replaced.

If you insert less items than you replace, the new items will be inserted where you specified, and the remaining items will move accordingly.

Example

Change the second and third value by replacing it with one value:

thislist = ["apple", "banana", "cherry"]

thislist[1:3] = ["watermelon"]

print(thislist)

Insert Items

To insert a new list item, without replacing any of the existing values, we can use the insert() method.

The insert() method inserts an item at the specified index.

Example

Insert "watermelon" as the third item:

thislist = ["apple", "banana", "cherry"]

thislist.insert(2, "watermelon")

print(thislist)

Note: As a result of the example above, the list will now contain 4 items.

14.3 Exercise

1. What will be the result of the following code:

mylist = ['apple', 'banana', 'cherry']

print(mylist[-1])

A. apple

B. banana

C. -1

D. cherry

2. Print the second item in the fruits list.

fruits = ["apple", "banana", "cherry"]

print(_______)

A. fruits[0]

B. fruits[1]

C. fruits[2]

D. fruits[-1]

3. What will be the result of the following code:

mylist = ['apple', 'banana', 'cherry', 'orange', 'kiwi']

print(mylist[1:4])

A. ['banana', 'cherry', 'orange']

B. ['banana', 'cherry', 'orange', 'kiwi']

C. ['cherry', 'orange', 'kiwi']

D. [1:4]

4. Use a range of indexes to print the third, fourth, and fifth item in the list.

fruits = ["apple", "banana", "cherry", "orange", "kiwi", "melon", "mango"]

print(fruits[______])

A. 3:5

B. 2:5

C. 2:4

D. 3:6

5. What will be the result of the following code:

mylist = ['apple', 'banana', 'cherry']

mylist[0] = 'kiwi'

print(mylist[1])

A. banana

B. cherry

C. apple

D. kiwi

6. What will be the result of the following code:

mylist = ['apple', 'banana', 'cherry']

mylist[1:2] = ['kiwi', 'mango']

print(mylist[2])

A. kiwi

B. mango

C. banana

D. cherry

7. Write a Python program to create a list to store student’s information, including: name, age, gender, GPA. Print the student’s information out following this pattern:

Information of Student:

[1] Name: Teo

[2] Age: 16

[3] Gender: male

[4] GPA: 3.0

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The answer hints:

1(D), 2(B), 3(A), 4(B), 5(A), 6(B)

7. Write a Python program to create a list to store student’s information, including: name, age, gender, GPA. Print the student’s information out following this pattern:

Information of Student:

[1] Name: Teo

[2] Age: 16

[3] Gender: male

[4] GPA: 3.0

[code14_7.py]

# Create a list to store student information

studentInfo = ["Teo", 16, "male", 3.0]

 

# Print the student's information

print("Information of Student:")

print(f"[1] Name: {studentInfo[0]}")

print(f"[2] Age: {studentInfo[1]}")

print(f"[3] Gender: {studentInfo[2]}")

print(f"[4] GPA: {studentInfo[3]}")

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Cập nhật: 31/10/2024

Bài sau: Python căn bản (15): Python Lists (cont.2)

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