Python Lists

A Python list is a versatile data structure that can store a collection of elements. It allows you to store items of different data types and offers dynamic resizing, making it a preferred choice for various programming tasks.

Creating and Initializing Lists

This section will cover the basic syntax for creating lists and various methods to initialize them with elements.

Empty List:

empty_list = []
another_empty_list = list()

List with Elements:

fruits = ['apple', 'banana', 'cherry']
numbers = [1, 2, 3, 4, 5]

Using a Loop:

squares = [x**2 for x in range(1, 6)] # Creates a list of the first five square numbers

List Comprehension:

even_numbers = [x for x in range(1, 11) if x % 2 == 0]

Repeating Elements:

zeroes = [0] * 5 # Creates a list with 5 zeroes

Using the range() Function:

numbers = list(range(1, 6)) # Creates a list of numbers from 1 to 5

Splitting a String:

sentence = "Hello, world!"
words = sentence.split(", ") # Splits the sentence into a list of words

Nested Lists:

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

Basic Operations on Lists

Learn how to perform fundamental operations on lists, such as finding the length, checking for elements, and slicing.

Accessing Elements: You can access individual elements in a list by their index. Remember that Python uses zero-based indexing, so the first element is at index 0.

my_list = [1, 2, 3, 4, 5] 
first_element = my_list[0] # Access the first element (1) 
third_element = my_list[2] # Access the third element (3)

</li>
<li>
<p><strong>Slicing Lists:</strong> You can extract a portion of a list using slicing. Slicing uses the format [start:stop:step], where start is the index to start from (inclusive), stop is the index to stop before (exclusive), and step is the interval between elements.</p>

```py
    my_list = [1, 2, 3, 4, 5] 
    sub_list = my_list[1:4] # Extracts elements from index 1 to 3: [2, 3, 4] 

```
</li>
<li>
<p><strong>Modifying Elements:</strong> Lists are mutable, so you can change the value of an element by assigning a new value to it.</p>

      my_list = [1, 2, 3, 4, 5] 
my_list[2] = 10 # Changes the third element to 10: [1, 2, 10, 4, 5]

</li>
<li>
<p><strong>Adding Elements:</strong> You can append elements to the end of a list using the append()method or extend a list by adding elements from another list using the extend()method.</p>

     my_list = [1, 2, 3] 
     my_list.append(4) # Appends 4 to the end: [1, 2, 3, 4] 
     my_list.extend([5, 6]) # Extends the list with [5, 6]: [1, 2, 3, 4, 5, 6] 
 ```
 <p><strong>Inserting Elements:</strong> You can insert an element at a specific index using the insert() method.</p>
<pre><code>
 my_list = [1, 2, 3, 4, 5] 
 my_list.insert(2, 10) # Inserts 10 at index 2: [1, 2, 10, 3, 4, 5] 
  </pre></code>
 <p><strong>Removing Elements:</strong> You can remove elements from a list by value using the remove() method, or by index using the pop() method.</p>
<pre><code>
 my_list = [1, 2, 3, 4, 5] 
 my_list.remove(3) # Removes the element with the value 3: [1, 2, 4, 5] 
 popped_element = my_list.pop(2) # Removes and returns the element at index 2 (4) 

  </pre></code>
 <p><strong>Checking for Existence:</strong> You can check if an element exists in a list using the in operator.</p>

  <pre><code>
  my_list = [1, 2, 3, 4, 5] exists = 3 in 
   </pre></code>
</ol>

<p>&nbsp; &nbsp; &nbsp;my_list # Checks if 3 exists in the list (True)</p>

<h3><strong>List Indexing and Slicing</strong></h3>

<p>Understand how indexing and slicing work with lists and explore examples of their practical usage.</p>

<p><strong>List Indexing:</strong> List indexing is the process of accessing a specific element in a list by specifying its position using an index. In Python, list indexing starts at 0 for the first element.</p>

<p>For example, if you have a list my_list, you can access elements as follows:</p>



<p>python code :</p>

<p><pre><code>

my_list = [10, 20, 30, 40, 50] 
element_at_index_0 = my_list[0] # Access the first element (10) 
element_at_index_2 = my_list[2] # Access the third element (30) 
element_at_index_minus_1 = my_list[-1] # Access the last element (50) 

</pre></code></p>

<p>In the above example, my_list[0] retrieves the first element, my_list[2] retrieves the third element, and my_list[-1] retrieves the last element. You can use both positive and negative indices to access elements.</p>

<p><strong>List Slicing:</strong> List slicing is the process of extracting a portion (sublist) of a list by specifying a range of indices. Slicing is done using the start:stop:step syntax, where:</p>

<ul>
 <li>start is the index at which the slice begins (inclusive).</li>
 <li>stop is the index at which the slice ends (exclusive).</li>
 <li>step is an optional argument that specifies the interval between elements (default is 1).</li>
</ul>

<p>Here&#39;s how list slicing works:</p>



<p>python code</p>

<p><pre><code>
my_list = [10, 20, 30, 40, 50] 
sublist = my_list[1:4] # Slices from index 1 to 4 (exclusive): [20, 30, 40] 
sublist_with_step = my_list[0:5:2] # Slices with a step of 2: [10, 30, 50] 
</pre></code></p>

<p>In the first example, my_list[1:4] extracts a sublist that includes elements at indices 1, 2, and 3 but not the element at index 4. In the second example, my_list[0:5:2]slices the list with a step of 2, which means it includes every second element.</p>



<h3><strong>&nbsp;Modifying Lists: Adding and Removing Elements</strong></h3>

<p>Explore methods to add new elements to lists and techniques to remove elements from lists.</p>


Adding Elements:

<p>Append: You can add an element to the end of a list using the append() method.</p>

<pre><code>
my_list = [1, 2, 3]
my_list.append(4)  # Adds 4 to the end of the list: [1, 2, 3, 4]
</pre></code>

<p>Extend: To add multiple elements to the end of a list, you can use the extend() method or the += operator.</p>
<pre><code>
my_list = [1, 2, 3]
my_list.extend([4, 5])  # Adds [4, 5] to the end: [1, 2, 3, 4, 5]
</pre></code>
<p>or</p>

<pre><code>
my_list += [4, 5]  # Adds [4, 5] to the end: [1, 2, 3, 4, 5]
</pre></code>

<p>Insert: To add an element at a specific index, you can use the insert() method.</p>
<pre><code>
my_list = [1, 2, 3]
my_list.insert(1, 4)  # Inserts 4 at index 1: [1, 4, 2, 3]
</pre></code>

Removing Elements:

<p>Remove: You can remove the first occurrence of a specific element using the remove() method.</p>
<pre><code>
my_list = [1, 2, 3, 2, 4]
my_list.remove(2)  # Removes the first occurrence of 2: [1, 3, 2, 4]
</pre></code>
<p>Pop: The pop() method removes and returns an element at a specified index. If the index is not provided, it removes and returns the last element by default.</p>
<pre><code>
my_list = [1, 2, 3, 4]
popped_element = my_list.pop()  # Removes and returns the last element (4)
element_at_index_1 = my_list.pop(1)  # Removes and returns the element at index 1 (2)
</pre></code>
<p>Del: The del statement can be used to remove an element or a slice of elements by specifying the index or range.</p>

<pre><code>
my_list = [1, 2, 3, 4]
del my_list[1]  # Removes the element at index 1: [1, 3, 4]
del my_list[1:3]  # Removes elements from index 1 to 2 (exclusive): [1, 4]
</pre></code>

<h3><strong>List Concatenation and Repetition</strong></h3>

<p>Discover how to combine multiple lists into one using concatenation and repetition techniques.</p>

<h3><strong>Iterating Through Lists</strong></h3>

<p>Learn different methods to iterate through lists and process elements efficiently.</p>

<h3><strong>List Comprehensions: A Concise Way to Create Lists</strong></h3>

<p>Discover the power of list comprehensions for generating lists in a concise and readable manner.</p>

<h3><strong>Sorting Lists: In-Place and Sorted Functions</strong></h3>

<p>Explore how to sort lists using both in-place sorting methods and the built-in &quot;sorted()&quot; function.</p>

<h3><strong>Common List Methods and Functions</strong></h3>

<p>This section will cover some commonly used list methods and functions for efficient data manipulation.</p>

<h3><strong>Nested Lists: Lists Within Lists</strong></h3>

<p>Understand how to create and work with nested lists, enabling more complex data structures.</p>

<h3><strong>List vs. Other Data Structures</strong></h3>

<p>Compare lists with other data structures like tuples, sets, and arrays to understand their unique use cases.</p>

<h3><strong>Best Practices for Using Python Lists</strong></h3>

<p>Learn best practices to write clean, Pythonic code using lists effectively.</p>

<h3><strong>Performance Considerations</strong></h3>

<p>Understand the performance implications of using lists for different tasks and how to optimize code.</p>

<h3><strong>Python List Gotchas: Pitfalls to Avoid</strong></h3>

<p>Explore common pitfalls and mistakes when working with lists and how to avoid them.</p>

```py
def getMedian(lst):
 sorted_lst = sorted(lst)
 n = len(sorted_lst)
 if n % 2 == 0:
     middle1 = sorted_lst[n // 2 - 1]
     middle2 = sorted_lst[n // 2]
     median = (middle1 + middle2) / 2
 else:
     median = sorted_lst[n // 2]
 return median


lst = [10, 50, 75, 83, 98, 84, 32,10]

#min value

print("min value :",min(lst))

print("max value :",max(lst))

print("mean value :",sum(lst)//len(lst))

print("median value :",getMedian(lst))

#Mode: The most frequent number—that is, the number that occurs the highest number
# of times.

print("mode value :",max(set(lst), key=lst.count))



from unittest import TestCase

class TestListOperations(TestCase):

 def test_minvalue(self):
     actual = min(lst)
     expected = 10
     self.assertEqual(actual, expected)

 def test_value(self):
     size=len(lst)
     self.assertTrue(size)

Python

Python Basics

Data Structures in Python

Python Core Concepts

Python Collections

Python Programs

Python Lists

Creating and Initializing Lists

Basic Operations on Lists