Lists

Lists¶

• Lists are used to store multiple items in a single variable.
• Lists can hold items of different data types such as string, integer, float

In [2]:

## creating a list
fruits_list = ['apple', 'banana', 'cherry', 10, 20, 30, 111.4]
print(fruits_list)

## creating a list fruits_list = ['apple', 'banana', 'cherry', 10, 20, 30, 111.4] print(fruits_list)

['apple', 'banana', 'cherry', 10, 20, 30, 111.4]

List is Mutable¶

In [3]:

fruits_list = ['apple', 'banana', 'cherry']
fruits_list[0] = 'mango'
print(fruits_list)

fruits_list = ['apple', 'banana', 'cherry'] fruits_list[0] = 'mango' print(fruits_list)

['mango', 'banana', 'cherry']

Indexing and Slicing¶

In [26]:

## creating the list
numbers_list = [53, 93, 35, 1, 65, 26, 47, 3]

## get the length of the list
print(len(numbers_list))

## creating the list numbers_list = [53, 93, 35, 1, 65, 26, 47, 3] ## get the length of the list print(len(numbers_list))

8

In [13]:

## indexing in list
print(numbers_list[0])
print(numbers_list[5])
print(numbers_list[-2])

## indexing in list print(numbers_list[0]) print(numbers_list[5]) print(numbers_list[-2])

53
26
47

In [4]:

## slicing in list
numbers_list = [53, 93, 35, 1, 65, 26, 47, 3]

## slicing with positive numbers
print('-----------------------------')
print('slicing with postive numbers')
print('-----------------------------')
print(numbers_list[1:4])     
print(numbers_list[:3])      
print(numbers_list[3:]) 

## slicing with negative numbers
print('-----------------------------')
print('slicing with negative numbers')
print('-----------------------------')
print(numbers_list[-5:-3])

## slicing in list numbers_list = [53, 93, 35, 1, 65, 26, 47, 3] ## slicing with positive numbers print('-----------------------------') print('slicing with postive numbers') print('-----------------------------') print(numbers_list[1:4]) print(numbers_list[:3]) print(numbers_list[3:]) ## slicing with negative numbers print('-----------------------------') print('slicing with negative numbers') print('-----------------------------') print(numbers_list[-5:-3])

-----------------------------
slicing with postive numbers
-----------------------------
[93, 35, 1]
[53, 93, 35]
[1, 65, 26, 47, 3]
-----------------------------
slicing with negative numbers
-----------------------------
[1, 65]

In [5]:

## with steps
numbers_list = [1, 2, 3, 4, 5, 6, 7, 8, 9]
print(numbers_list[::2])

## reverse the list
print(numbers_list[::-1])   

## with steps numbers_list = [1, 2, 3, 4, 5, 6, 7, 8, 9] print(numbers_list[::2]) ## reverse the list print(numbers_list[::-1])

[1, 3, 5, 7, 9]
[9, 8, 7, 6, 5, 4, 3, 2, 1]

In [6]:

temp_list = ['apple', 1, 2]

temp_list = ['apple', 1, 2]

In [10]:

a = 2
print(type(temp_list))

a = 2 print(type(temp_list))

<class 'list'>

List Methods¶

Method	Description	Example Code	Output
append()	Adds an item to the end of the list	lst = [1, 2] lst.append(3)	[1, 2, 3]
extend()	Adds all elements of another list	lst = [1, 2] lst.extend([3, 4])	[1, 2, 3, 4]
insert()	Inserts item at given index	lst = [1, 3] lst.insert(1, 2)	[1, 2, 3]
remove()	Removes first occurrence of value	lst = [1, 2, 3] lst.remove(2)	[1, 3]
pop()	Removes and returns item at index (default last)	lst = [1, 2, 3] lst.pop()	3, list: [1, 2]
clear()	Removes all items from the list	lst = [1, 2, 3] lst.clear()	[]
index()	Returns first index of value	lst = [10, 20, 30] lst.index(20)	1
count()	Counts how many times value appears	lst = [1, 1, 2, 1] lst.count(1)	3
sort()	Sorts the list in ascending order	lst = [3, 1, 2] lst.sort()	[1, 2, 3]
reverse()	Reverses the order of the list	lst = [1, 2, 3] lst.reverse()	[3, 2, 1]
copy()	Returns a shallow copy of the list	lst = [1, 2] new = lst.copy()	new = [1, 2]

In [25]:

# List of cities
cities = [
    "Kathmandu",
    "New York",
    "Tokyo",
    "Paris",
    "London",
    "Sydney",
    "Dubai",
    "Toronto",
    "Rome",
]

# List of cities cities = [ "Kathmandu", "New York", "Tokyo", "Paris", "London", "Sydney", "Dubai", "Toronto", "Rome", ]

In [26]:

cities.sort()
print(cities)

cities.sort() print(cities)

['Dubai', 'Kathmandu', 'London', 'New York', 'Paris', 'Rome', 'Sydney', 'Tokyo', 'Toronto']

In [27]:

cities.sort(reverse=True)
print(cities)

cities.sort(reverse=True) print(cities)

['Toronto', 'Tokyo', 'Sydney', 'Rome', 'Paris', 'New York', 'London', 'Kathmandu', 'Dubai']

In [19]:

removed_element = cities.pop(1)
print(removed_element)

removed_element = cities.pop(1) print(removed_element)

New York

In [20]:

print(cities)

print(cities)

['Kathmandu', 'Tokyo', 'Paris', 'London', 'Sydney', 'Dubai', 'Toronto', 'Rome']

In [12]:

cities.append('Pokhara')

cities.append('Pokhara')

In [13]:

print(cities)

print(cities)

['Kathmandu', 'New York', 'Tokyo', 'Paris', 'London', 'Sydney', 'Dubai', 'Toronto', 'Rome', 'Pokhara']

In [29]:

# List of cities
cities = [
    "Kathmandu",
    "New York",
    "Tokyo",
    "Paris",
    "London",
    "Sydney",
    "Dubai",
    "Toronto",
    "Rome",
]

print(cities.sort())

# List of cities cities = [ "Kathmandu", "New York", "Tokyo", "Paris", "London", "Sydney", "Dubai", "Toronto", "Rome", ] print(cities.sort())

None

In [30]:

print(cities)

print(cities)

['Dubai', 'Kathmandu', 'London', 'New York', 'Paris', 'Rome', 'Sydney', 'Tokyo', 'Toronto']

In [31]:

help(cities.sort)

help(cities.sort)

Help on built-in function sort:

sort(*, key=None, reverse=False) method of builtins.list instance
    Sort the list in ascending order and return None.

    The sort is in-place (i.e. the list itself is modified) and stable (i.e. the
    order of two equal elements is maintained).

    If a key function is given, apply it once to each list item and sort them,
    ascending or descending, according to their function values.

    The reverse flag can be set to sort in descending order.

In [16]:

## insert
a = [1, 2, 3, 5]
a.insert(5,1)
print(a)

## insert a = [1, 2, 3, 5] a.insert(5,1) print(a)

[1, 2, 3, 5, 1]

In [17]:

help(list.insert)

help(list.insert)

Help on method_descriptor:

insert(self, index, object, /) unbound builtins.list method
    Insert object before index.

In [12]:

cities.sort(reverse=True)
print(cities)

cities.sort(reverse=True) print(cities)

['Toronto', 'Tokyo', 'Sydney', 'Rome', 'Pokhara', 'Paris', 'New York', 'London', 'Kathmandu', 'Dubai']

Exercise : Create list of atleast 7 favorite movies or series.¶

• Print the second and last movies.
• Print from second to second last movies
• Reverse the list.
• Add a new movie.
• Sort the list alphabetically.
• Remove the third movie
• clear all the list

Shallow Copy vs Deep Copy¶

• A shallow copy creates a new outer object, but doesn't copy nested objects inside it.

• Both the original and the copy share references to the same inner objects.

In [32]:

original_list = [[1, 2], [3, 4], ['apple', 'mango', 'coconut']]

## shallow copy of the list
copy_list = original_list.copy()

print(original_list)
print(copy_list)

original_list = [[1, 2], [3, 4], ['apple', 'mango', 'coconut']] ## shallow copy of the list copy_list = original_list.copy() print(original_list) print(copy_list)

[[1, 2], [3, 4], ['apple', 'mango', 'coconut']]
[[1, 2], [3, 4], ['apple', 'mango', 'coconut']]

In [33]:

copy_list[2][0]

copy_list[2][0]

Out[33]:

'apple'

In [34]:

copy_list[0][0] = 5

print(original_list)
print(copy_list)

copy_list[0][0] = 5 print(original_list) print(copy_list)

[[5, 2], [3, 4], ['apple', 'mango', 'coconut']]
[[5, 2], [3, 4], ['apple', 'mango', 'coconut']]

In [35]:

## an example of deep copy
import copy
original_list = [[1, 2], [3, 4]]

deep_copy_list = copy.deepcopy(original_list)
deep_copy_list[0][0] = 5

print(original_list)
print(deep_copy_list)

## an example of deep copy import copy original_list = [[1, 2], [3, 4]] deep_copy_list = copy.deepcopy(original_list) deep_copy_list[0][0] = 5 print(original_list) print(deep_copy_list)

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

In [ ]: