Python - Lists
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In Python, a list is a mutable, ordered collection of elements. Each element can be of any data type, and the elements are enclosed within square brackets []. Lists allow for easy storage and manipulation of data.
Here's an example program that demonstrates the basic usage of lists:
# Creating a list
my_list = [1, 2, 3, 'four', 5.0]
# Accessing elements in a list
print(my_list[0]) # Output: 1
print(my_list[3]) # Output: 'four'
# Modifying elements in a list
my_list[1] = 'two'
print(my_list) # Output: [1, 'two', 3, 'four', 5.0]
# Adding elements to a list
my_list.append(6)
print(my_list) # Output: [1, 'two', 3, 'four', 5.0, 6]
# Removing elements from a list
my_list.remove('four')
print(my_list) # Output: [1, 'two', 3, 5.0, 6]
# List slicing
subset = my_list[1:4]
print(subset) # Output: ['two', 3, 5.0]
The above program initializes a list, accesses and modifies its elements, adds new elements, removes an element, and demonstrates list slicing.
Outputs:
1 'four' [1, 'two', 3, 'four', 5.0] [1, 'two', 3, 'four', 5.0, 6] [1, 'two', 3, 5.0, 6] ['two', 3, 5.0]
To create an empty list in Python, you can use the square brackets with no elements between them. Here's an example program demonstrating how to create an empty list:
# Creating an empty list
empty_list = []
# Checking the type and content of the list
print(type(empty_list)) # Output: <class 'list'>
print(empty_list) # Output: []
The program initializes an empty list and then uses the type() function to confirm that it is indeed a list. Finally, it prints the empty list.
Output:
<class 'list'> []
Lists and tuples are both data structures in Python, but they have some key differences. Here's an explanation along with an example program:
Lists:
A list is a mutable, ordered collection of elements. Mutable means that you can change the elements of a list after it is created. Lists are defined using square brackets [].
# Creating a list
my_list = [1, 2, 3, 'four', 5.0]
# Modifying elements in a list
my_list[1] = 'two'
print(my_list) # Output: [1, 'two', 3, 'four', 5.0]
Tuples:
A tuple is an immutable, ordered collection of elements. Immutable means that once a tuple is created, you cannot modify its elements. Tuples are defined using parentheses ( ).
# Creating a tuple
my_tuple = (1, 2, 3, 'four', 5.0)
# Attempting to modify elements in a tuple (will result in an error)
# my_tuple[1] = 'two' # Uncommenting this line will raise a TypeError
The key difference is that lists are mutable, allowing for modification of elements, while tuples are immutable, preventing any changes after creation.
Outputs:
[1, 'two', 3, 'four', 5.0]
In Python, elements in a list are accessed using indexing. Indexing starts from 0 for the first element and goes up to len(list) - 1 for the last element. Here's an example program demonstrating how to access elements in a list:
# Creating a list
my_list = [1, 2, 3, 'four', 5.0]
# Accessing elements using positive indexing
first_element = my_list[0]
third_element = my_list[2]
last_element = my_list[-1]
print(first_element) # Output: 1
print(third_element) # Output: 3
print(last_element) # Output: 5.0
# Accessing elements using negative indexing
second_to_last_element = my_list[-2]
print(second_to_last_element) # Output: four
The program initializes a list and demonstrates accessing elements using both positive and negative indexing. Positive indexing starts from the beginning of the list, while negative indexing starts from the end.
Outputs:
1 3 5.0 four