Python Lists¶
Python lists are highly flexible data structures that allow you to store a sequence of items. These items can be of any data type, including numbers, strings, and even other lists, making Python lists very versatile for various programming tasks.
Creating a List¶
To create a list in Python, you enclose items in square brackets [ ], separating each item with a comma:
# Creating a list of days
days = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday"]
# Creating a list with mixed data types
mixed_list = ['abc', 67, True, 3.14, "female"]
You can also use the list() constructor to create a list:
# Creating a list using the list() constructor
list_cons = list(("hello", "world", "beautiful", "day"))
list_cons
['hello', 'world', 'beautiful', 'day']
Accessing List Elements¶
List elements are accessed by their index, which starts at 0 for the first element. You can also use negative indices to access elements from the end of the list:
print(days[0]) # Outputs 'Sunday'
print(mixed_list[-1]) # Outputs 'female'
Sunday female
Modifying Lists¶
Lists are mutable, meaning you can change their elements:
days[3] = "Friday" # Changes 'Wednesday' to 'Friday'
days
['Sunday', 'Monday', 'Tuesday', 'Friday', 'Thursday']
Adding and Removing Elements¶
To add elements to a list, you can use the append() method for single items or extend() for adding multiple items:
days.append('Saturday') # Adds 'Saturday' to the end
days.extend(['ExtraDay1', 'ExtraDay2']) # Adds two more days at the end
days
['Sunday', 'Monday', 'Tuesday', 'Friday', 'Thursday', 'Saturday', 'ExtraDay1', 'ExtraDay2', 'Saturday', 'ExtraDay1', 'ExtraDay2']
To remove elements, use the remove() method to remove by value, or pop() to remove by index:
days.remove('ExtraDay1') # Removes 'ExtraDay1'
days.pop(0) # Removes the first element ('Sunday')
'Sunday'
List Length¶
To find the number of items in a list, use the len() function:
print(len(days)) # Outputs the number of items in the days list
9
Slicing Lists¶
You can get a sublist of items by slicing the list using the : operator:
weekdays = days[1:5] # Gets items from index 1 to 4
weekdays
['Tuesday', 'Friday', 'Thursday', 'Saturday']
Nested Lists¶
Lists can contain other lists as elements, allowing for multi-dimensional arrays:
nested_list = ["hello", [8, 4, 6], ['world']]
nested_list
['hello', [8, 4, 6], ['world']]
Checking for Existence¶
To check if an item exists in a list, use the in operator:
print("Tuesday" in days) # Outputs True if 'Tuesday' is in the list
True
Finding Minimum and Maximum¶
For lists containing comparable items, you can find the smallest and largest items with min() and max():
numbers = [1, 2, 3, 4, 5]
print(min(numbers)) # Outputs the smallest number
print(max(numbers)) # Outputs the largest number
1 5
List Comprehensions¶
List comprehension in Python is a concise way to create lists. It allows you to generate a new list by applying an expression to each item in an existing iterable (like a list, tuple, or string) in a single line of code. For example, to create a list of square numbers:
squares = [x**2 for x in range(10)]
squares
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
Conclusion¶
Python lists are a powerful and integral part of Python programming. They offer flexibility in storing, accessing, and manipulating collections of data. By mastering Python lists, you enhance your capability to solve a wide range of programming problems efficiently.