<h5 id="91-introduction-to-list">9.1 INTRODUCTION TO LIST</h5> <ul> <li>A list is an ordered sequence, which is mutable and made up of one or more elements.</li> <li>Elements of a list can be of different data types, such as integer, float, string, tuple or even another list.</li> <li>Elements of a list are enclosed in square brackets and are separated by commas.</li> <li>List indices start from 0, similar to string indices.</li> <li>An example of a list of lists (nested list) is: [[‘Physics’,101],[‘Chemistry’,202],[‘Maths’,303]].</li> </ul> <p>======</p> <h5 id="911-accessing-elements-in-a-list">9.1.1 Accessing Elements in a List</h5> <ul> <li>The elements of a list are accessed similarly to characters in a string, using an integer index.</li> <li>Accessing an index that is out of range will return an error, for example, list1[15] would return an error for list1 = [2,4,6,8,10,12].</li> <li>You can access elements from the right of the list by using negative indexing, for example, list1[-1] would return the last element of list1.</li> <li>The length of the list can be found using the len() function, for example, n = len(list1) would find the length of list1.</li> <li>The first and last elements of the list can be accessed using list1[0] and list1[-1] or list1[len(list1)-1] respectively.</li> </ul> <p>======</p> <h5 id="912-lists-are-mutable">9.1.2 Lists are Mutable</h5> <ul> <li>In Python, lists are mutable data structures.</li> <li>This means the contents of a list can be changed after its creation.</li> <li>For example, you can change the fourth element of a list called list1: <code>list1[3] = 'Black'</code>.</li> <li>Before the change, list1 contained the colors ‘Red’, ‘Green’, ‘Blue’, and ‘Orange’.</li> <li>After the change, the fourth element of list1 is now ‘Black’: <code>list1 = ['Red', 'Green', 'Blue', 'Black']</code>.</li> </ul> <p>======</p> <h5 id="92-list-operations">9.2 LIST OPERATIONS</h5> <ul> <li>List operations include methods for adding, removing, and reordering elements within a list.</li> <li>The <code>append()</code> method adds a single item to the existing list, while the <code>extend()</code> method adds elements from another list or iterable object.</li> <li>The <code>remove()</code> method deletes the first occurrence of a specific value, and the <code>pop()</code> method removes and returns the item at a specified position.</li> <li>The <code>insert()</code> method inserts an item at a specified position, and the <code>sort()</code> method arranges all elements in ascending order.</li> <li>The <code>reverse()</code> method reverses the order of elements in a list, and the <code>copy()</code> method creates a shallow copy of the original list.</li> </ul> <p>======</p> <h5 id="921-concatenation">9.2.1 Concatenation</h5> <ul> <li>In Python, lists can be joined using the concatenation operator <code>+</code>.</li> <li>The concatenation operator requires that the operands should be of list type only. Concatenating a list with elements of another data type will result in a <code>TypeError</code>.</li> <li>There is no change in the original lists after the concatenation operation. If you want to merge two lists, an assignment statement should be used.</li> <li>For example, <code>list1 + list2</code> will result in a new list containing elements of <code>list1</code> followed by elements of <code>list2</code>.</li> <li>The <code>type()</code> function can be used to confirm if the operands are of list type. For instance, <code>type([1, 2, 3])</code> will return <code><class 'list'></code>.</li> </ul> <p>======</p> <h5 id="922-repetition">9.2.2 Repetition</h5> <ul> <li>Python allows repetition of lists using the repetition operator, denoted by the symbol ‘*’.</li> <li>For example, if list1 = [‘Hello’], then list1 * 4 will result in [‘Hello’, ‘Hello’, ‘Hello’, ‘Hello’].</li> <li>The number of repetitions can be any positive integer.</li> <li>This feature can be useful when creating new lists with repeated elements.</li> <li>No equations or formulae are provided in this text.</li> </ul> <p>======</p> <h5 id="923-membership">9.2.3 Membership</h5> <ul> <li>Membership operators in Python are used to check if an element is present in a list.</li> <li>The “in” operator returns True if the element is present in the list, and False otherwise. For example, ‘Green’ is in [‘Red’,‘Green’,‘Blue’] returns True.</li> <li>The ’not in’ operator returns True if the element is not present in the list, and False otherwise. For example, ‘Cyan’ is not in [‘Red’,‘Green’,‘Blue’] returns True.</li> <li>Lists are ordered collections of data, and the membership operators check for the presence or absence of an element at any position in the list.</li> <li>The membership operators can be used with any type of data supported by Python, including numbers, strings, and custom objects.</li> </ul> <p>======</p> <h5 id="924-slicing">9.2.4 Slicing</h5> <ul> <li>The slicing operation applicable to strings can also be applied to lists.</li> <li>The syntax for slicing a list is: list_name[start_index:end_index].</li> <li>If the second index is out of range, it will result in an error (e.g. list1[2:20] will result in an error if list1 has less than 20 elements).</li> <li>If the first index is greater than the second index, it will result in an empty list (e.g. list1[7:2] will result in an empty list).</li> <li>The step size can also be specified in the slicing operation, for example list1[0:6:2] will return every second element from index 0 to 6.</li> <li>Negative indexes can be used to slice elements from the end of the list, for example list1[-6:-2] will return elements at index -6, -5, -4, and -3.</li> <li>Negative step size can be used to reverse the order of the list, for example list1[::-1] will return the list in reverse order.</li> </ul> <p>======</p> <h5 id="93-traversing-a-list">9.3 TRAVERSING A LIST</h5> <ul> <li>List traversal is accessing each element of a list, which can be done using for loop or while loop.</li> <li>For list traversal using for loop, Python’s in keyword is used to iterate over the elements of the list.</li> <li>The length of the list can be obtained using the len() function, and this can be used to access the elements using range() and len() functions with a for loop.</li> <li>For list traversal using while loop, an index variable is used to access the elements of the list, and the loop continues until the index is less than the length of the list.</li> <li>In both methods, the elements of the list are accessed and printed one at a time, resulting in the same output.</li> </ul> <p>======</p> <h5 id="94-list-methods-and-built-in-functions">9.4 LIST METHODS AND BUILT-IN FUNCTIONS</h5> <ul> <li>The <code>len()</code> function returns the length of a list.</li> <li>The <code>list()</code> function creates an empty list or converts a sequence into a list.</li> <li>The <code>append()</code> function adds an element to the end of a list, which can be a single element or another list.</li> <li>The <code>extend()</code> function adds multiple elements from another list to the end of the given list.</li> <li>The <code>insert()</code> function inserts an element at a specific index in the list.</li> <li>The <code>count()</code> function returns the number of times a given element appears in the list.</li> <li>The <code>index()</code> function returns the index of the first occurrence of an element in the list.</li> <li>The <code>remove()</code> function removes the first occurrence of an element from the list.</li> <li>The <code>pop()</code> function returns and removes an element from the list based on the provided index; if no index is provided, it removes and returns the last element.</li> <li>The <code>reverse()</code> function reverses the order of elements in the list.</li> <li>The <code>sort()</code> function sorts the elements of the list in-place.</li> <li>The <code>sorted()</code> function creates a new sorted list from the elements of the given list.</li> <li>The <code>min()</code> function returns the smallest element in the list, while the <code>max()</code> function returns the largest element.</li> <li>The <code>sum()</code> function returns the sum of all elements in the list.</li> </ul> <p>======</p> <h5 id="95-nested-lists">9.5 NESTED LISTS</h5> <ul> <li>A list within a list is referred to as a nested list.</li> <li>To access an element in a nested list, two indices are required: list[i][j], where i is the index of the nested list and j is the index of the desired element in that nested list.</li> <li>For example, in list1 = [1,2,‘a’,‘c’,[6,7,8],4,9], list1[4][1] would return 7, where 4 is the index of the nested list [6,7,8] and 1 is the index of the element 7.</li> <li>The first index i allows you to access the desired nested list, while the second index j allows you to access the desired element in that nested list.</li> <li>This structure is useful for organizing and accessing data in a hierarchical or multi-layered manner.</li> </ul> <p>======</p> <h5 id="96-copying-lists">9.6 COPYING LISTS</h5> <ul> <li>The simplest way to copy a list in Python is by assigning it to another list. However, this creates an alias, not a distinct object.</li> <li>A copy or clone of a list as a distinct object can be created using three methods: slicing, built-in function list(), and copy() function of python library.</li> <li>In the slicing method, the original list is sliced and stored into a new variable. For example, newList = oldList[:].</li> <li>The built-in function list() can be used to create a copy of the list. For example, newList = list(oldList).</li> <li>The copy() function of the python library copy can also be used to create a copy. For example, newList = copy.copy(oldList).</li> </ul> <p>======</p> <h5 id="97-list-as-argument-to-a-function">9.7 LIST AS ARGUMENT TO A FUNCTION</h5> <ul> <li>When a list is passed as an argument to a function, any changes made to the list within the function will be reflected back to the calling function.</li> <li>This is because a reference to the list is passed, not a new list.</li> <li>However, if a new list is assigned to the list within the function, a new list object is created and any changes made to this new list will not affect the original list.</li> <li>This is because the new list is a local copy of the function and any changes made to it will not be reflected back to the calling function.</li> <li>In summary, when passing a list as an argument to a function, changes to the list will be reflected back to the calling function, unless a new list is assigned within the function, in which case the new list will be a local copy and any changes made to it will not affect the original list.</li> </ul> <p>======</p> <h5 id="98-list-manipulation">9.8 LIST MANIPULATION</h5> <ul> <li>Program 9-3 is a menu-driven program that performs various list operations such as:</li> </ul> <ol> <li>Appending an element to the list</li> <li>Inserting an element at a desired position</li> <li>Appending a list to the given list</li> <li>Modifying an existing element</li> <li>Deleting an existing element by its position</li> <li>Deleting an existing element by its value</li> <li>Sorting the list in ascending order</li> <li>Sorting the list in descending order</li> <li>Displaying the list</li> </ol> <ul> <li> <p>The user can interact with the program through a numbered menu, selecting which operation to perform.</p> </li> <li> <p>The program uses the <code>append()</code>, <code>insert()</code>, <code>extend()</code>, <code>pop()</code>, and <code>sort()</code> list methods to manipulate the list.</p> </li> <li> <p>The user can also exit the program by selecting option 10.</p> </li> <li> <p>Program 9-4 calculates the average marks of n students using a function.</p> </li> <li> <p>The user is asked to input the number of students (n), and then the marks for each student are input and stored in a list.</p> </li> <li> <p>The <code>computeAverage()</code> function calculates the average marks of the students by summing the elements in the list and dividing by n.</p> </li> <li> <p>The average marks are then printed.</p> </li> <li> <p>Program 9-5 defines a function <code>linearSearch()</code> that checks if a number is present in a list or not.</p> </li> <li> <p>If the number is present, the function returns its position in the list.</p> </li> <li> <p>If the number is not present, the function returns <code>None</code>.</p> </li> <li> <p>The user inputs the list elements and the number to be searched.</p> </li> <li> <p>The function is called with the list and number as arguments, and the output is printed.</p> </li> </ul> <p>======</p>