Data Collction - List 列表 (list) []

• We will using data collection method to store all the data in that specific category.

Properties of list:

• list allow repeat data

Syntax

Define list

# Literal
["John", "Ben"]

# With variable name
student_list = ["John", "Ben"]

Define Empty list

empty_list_1 = []
empty_list_2 = list()

Get item in a list

student_list = ["John", "Ben"]

print(student_list[0]) # John

# Index of list start at 0

INFO

• If the index of the list is from left to right, it follow positive int index, 0, 1, 2, ...
• If its from right to left it become -1, -2, -3, .... (negative int)
• - 0 = + 0

Method of list

Basic Introduction of method

• method in python means a function define in a class.
• Different of usage between class and function:

Way of define

# Function
def add(x, y):
    return x + y

# Method
class Maths:

    def add(x, y):
        return x + y

Way of usage:

# Function
print(add(1, 2))

# Method
maths = Maths()
print(maths.add(1, 2))

1. Find index of an item in list (list.index(value))

list-method.py

name_list = ["Ben", "John", "Kai", "Alpha", "Elen"]
#             0,      1,      2,      3,       4

# 1. Find index of an item in a list
print(f"Index of 'John' in list is at {name_list.index("John")} ") # 1

Results:

Index of 'John' in list is at 1

2. Update of an element in list (list_name[index] = new_value)

list-method.py

# 2. Update of an element in list
# Update Elen -> Alen
name_list[4] = "Alen" 
print(name_list)

Results:

['Ben', 'John', 'Kai', 'Alpha', 'Alen']

3. Insert an new item to the list at specific position (list.insert(position_index, object))

• insert index number will be a index number of old list, if the item is already exist.

list-method.py

# 3. Add an new element to specific position
# ['Ben', 'John', 'Kai', 'Alpha', 'Alen']
name_list.insert(2, "Lame")
print(name_list)

Results:

['Ben', 'John', 'Lame', 'Kai', 'Alpha', 'Alen']

4. Insert an item at the end of the list (list.append())

list-method.py

# ['Ben', 'John', 'Lame', 'Kai', 'Alpha', 'Alen']

# 4. add new item at the end of the list.
name_list.append("Julie")
print(name_list)

Results:

['Ben', 'John', 'Lame', 'Kai', 'Alpha', 'Alen', 'Julie']

5. Extend a new List of item to a list (list.extend())

list-method.py

# ['Ben', 'John', 'Lame', 'Kai', 'Alpha', 'Alen', 'Julie']
# 5. add a list of item to a list
new_student_list = ["Ali", "bob"]
name_list.extend(new_student_list)
print(name_list)

Results:

['Ben', 'John', 'Lame', 'Kai', 'Alpha', 'Alen', 'Julie', 'Ali', 'bob']

6. Remove item in a list (del list[index] / list.pop(index))

• list.pop() by default will remove last item in a list if no index is mentioned.

list-method.py

# 6. Delete item in a list

# ['Ben', 'John', 'Lame', 'Kai', 'Alpha', 'Alen', 'Julie', 'Ali', 'bob']
# Remove item at the last
name_list.pop() 
print(name_list) 

# ['Ben', 'John', 'Lame', 'Kai', 'Alpha', 'Alen', 'Julie', 'Ali']
name_list.pop(0) # Remove Ben
print(name_list)

# ['John', 'Lame', 'Kai', 'Alpha', 'Alen', 'Julie', 'Ali']
# another method of delete item in a list
del name_list[3] # Remove Alpha
print(name_list)
# ['John', 'Lame', 'Kai', 'Alen', 'Julie', 'Ali']

Results:

['Ben', 'John', 'Lame', 'Kai', 'Alpha', 'Alen', 'Julie', 'Ali']
['John', 'Lame', 'Kai', 'Alpha', 'Alen', 'Julie', 'Ali']
['John', 'Lame', 'Kai', 'Alen', 'Julie', 'Ali']

7. Remove based on the value in a list (list.remove(match_value))

list-method.py

# 7. remove an item based on the match value
# ['John', 'Lame', 'Kai', 'Alen', 'Julie', 'Ali']
name_list.remove("Lame") # remove Lame
print(name_list)

Results:

['John', 'Kai', 'Alen', 'Julie', 'Ali']

8. Clear all item in a list (list.clear())

list-method.py

# 8. clear entire list
# ['John', 'Kai', 'Alen', 'Julie', 'Ali']
name_list.clear()
print(name_list)

Results:

[]

9. Find a count of an item in a list (list.count(match_value))

list-method.py

################################
# Create a new list with the random number from a dice
################################

dice_num_gets = [1, 6, 3, 1, 1, 2, 5, 4, 6, 6, 3, 2]

# 9. Get a items count
# num of getting 1 in a from a dice roll gets
print(dice_num_gets.count(1)) # 3 (3 "1" in a list)

Results:

3

Conclusion and overall code

Methods	Description
list.index()	Get the index number of an item in a list based on the item.
list.insert()	Add an new item into a list.
list.append()	Add an new item at the end of a list.
list.extends([])	Add an list [] of item at the end of a list.
list.[index] = value	Update an item in a list.
list.pop()	Delete an new item into a list. Default: last item
del list_name[index]	Delete an item into a list, it follow the index number
list.remove()	Delete an item into a list, it follow the index number based on the item
list.clear()	Clear entire list

Overall code: list-method.py

Click to expand

name_list = ["Ben", "John", "Kai", "Alpha", "Elen"]
#             0,      1,      2,      3,       4

# 1. Find index of an item in a list
print(f"Index of 'John' in list is at {name_list.index("John")} ") # 1

# 2. Update of an element in list
# Update Elen -> Alen

name_list[4] = "Alen"
print(name_list)

# 3. Add an new element to specific position
# Note that current name_list =
# ['Ben', 'John', 'Kai', 'Alpha', 'Alen']

name_list.insert(2, "Lame")
print(name_list)

# ['Ben', 'John', 'Lame', 'Kai', 'Alpha', 'Alen']
# 4. add new item at the end of the list.
name_list.append("Julie")
print(name_list)

# ['Ben', 'John', 'Lame', 'Kai', 'Alpha', 'Alen', 'Julie']
# 5. add a list of item to a list
new_student_list = ["Ali", "bob"]
name_list.extend(new_student_list)
print(name_list)

# 6. Delete item in a list

# ['Ben', 'John', 'Lame', 'Kai', 'Alpha', 'Alen', 'Julie', 'Ali', 'bob']
# Remove item at the last
name_list.pop() 
print(name_list) 

# ['Ben', 'John', 'Lame', 'Kai', 'Alpha', 'Alen', 'Julie', 'Ali']
name_list.pop(0) # Remove Ben
print(name_list)

# ['John', 'Lame', 'Kai', 'Alpha', 'Alen', 'Julie', 'Ali']
# another method of delete item in a list
del name_list[3] # Remove Alpha
print(name_list)
# ['John', 'Lame', 'Kai', 'Alen', 'Julie', 'Ali']

Useful Built-in Functions for Lists

Function	Description
len(list)	Get number of items
max(list)	Largest value
min(list)	Smallest value
sum(list)	Sum of numbers
sorted(list)	Return sorted copy
list()	Convert iterable to list

Scenario based usage

Checking if Item Exists

• use match_value in list_name to get a Boolean value.

numbers = [1, 2, 3]

print(2 in numbers)
# True

Slicing

numbers = [1, 2, 3, 4, 5]

print(numbers[1:4])
# 1 -> 4 (3 items) from index 1 start
# [2, 3, 4]

A short way to create lists.

squares = [x * x for x in range(5)]

print(squares)
# [0, 1, 4, 9, 16]

Usage

• Partialy usage only...

list.py

student_list = ["Ben", "John", "Kai", "Alpha", "Elen"]

# Print entire list
print(student_list)
# Type of list
print(type(student_list))

# print follow the index of the list
# First Items
print(f"The first student = {student_list[0]}")
# Last items
print(f"The last student = {student_list[-1]}")
# or
print(f"The last student = {student_list[4]}")

# Total items in the list
print(f"Length of the list = {len(student_list)}")

# Index of Ben
print(student_list.index("Ben")) # 0 (first item)

# Add an new name at the end
student_list.append("Bob")
print(student_list)

# Add a name in front of Bob (index of bob: 5)
# Note bob position at 5 in new item added then bob will be at 6, 5 will be kay
student_list.insert(5, "Kay")
print(student_list)

new_comers = ["Ola", "Lynn"]
student_list.extend(new_comers)
print(student_list)

# Ben and John withdraw
# index of, ben = 0, john = 1
del student_list[0]
student_list.pop(1)
print(student_list)

# Ola replaced by another students - Lu
# Ola index number = 5 
student_list[5] = "Lu"
print(student_list)

Results:

['Ben', 'John', 'Kai', 'Alpha', 'Elen']
<class 'list'>
The first student = Ben
The last student = Elen
The last student = Elen
Length of the list = 5
0
['Ben', 'John', 'Kai', 'Alpha', 'Elen', 'Bob']
['Ben', 'John', 'Kai', 'Alpha', 'Elen', 'Kay', 'Bob']
['Ben', 'John', 'Kai', 'Alpha', 'Elen', 'Kay', 'Bob', 'Ola', 'Lynn']
['John', 'Alpha', 'Elen', 'Kay', 'Bob', 'Ola', 'Lynn']
['John', 'Alpha', 'Elen', 'Kay', 'Bob', 'Lu', 'Lynn']