Create Nested list using function | Python Essentials

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4 Sept 202206:39

Summary

TLDRIn this Python essentials video, Nikhil demonstrates how to create a nested list in Python. He starts by defining a function that generates a list of numbers from 0 to 9. Then, using a while loop, he initializes an empty list called 'nest_list' and uses the 'append' method to create a nested list structure with 10 lists, each containing numbers from 0 to 9. The video clarifies the difference between using 'extend' and 'append' for creating nested lists.

Takeaways

📝 The video explains how to create a nested list using Python lists, loops, and functions.
🧑‍🏫 The speaker mentions that using arrays would make this easier, but the example focuses on using Python lists.
🛠️ A user-defined function is used to generate a single list with values from 0 to 9.
⚙️ The function has no arguments and initializes an empty list, then appends values in a range of 0 to 9 using a for loop.
🔄 The video suggests an alternative approach using a while loop to create a similar list.
📑 The `extend()` function adds individual elements from the list to the main list, leading to a non-nested result.
📌 To create a nested list, the speaker switches to the `append()` method, which adds each generated list as an element within the main list.
🔢 The final nested list has 10 sub-lists, each containing numbers 0 to 9, as intended.
💡 The video contrasts the usage of `extend()` and `append()` to show how they affect the list structure differently.
✅ By using `append()`, the desired result of 10 lists nested within a larger list is achieved.

Q & A

What is the purpose of the video?
-The video aims to teach viewers how to create a nested list in Python using lists and functions.
What data structure does the video focus on, and why?
-The video focuses on lists because Python does not have arrays in the traditional sense, so nested lists are used to create multi-dimensional structures.
What is the first step in creating a nested list as explained in the video?
-The first step is to define a function that generates a single list containing the values 0 to 9.
How does the function 'listnum' generate the list?
-The function 'listnum' initializes an empty list, then uses a 'for' loop to iterate from 0 to 9, appending each value to the list, and finally returns the list.
Why does the function not take any arguments?
-The function does not require any arguments because it generates a predefined list of values (0 to 9), making input parameters unnecessary.
What mistake did the video highlight when trying to create a nested list using 'extend'?
-Using 'extend' caused the elements of each list to be added to a single list continuously, instead of creating a true nested list. 'Extend' merges elements, which prevents the formation of separate lists within the parent list.
What change is needed to correctly create a nested list?
-To correctly create a nested list, 'append' should be used instead of 'extend', which ensures that each list is added as an individual element to the main list.
What is the result when 'append' is used instead of 'extend'?
-When 'append' is used, the output is a nested list where each inner list (containing values 0 to 9) is a separate element, repeated 10 times.
How is the while loop used in creating the nested list?
-The while loop is used to repeatedly append the list generated by 'listnum' to the main nested list, iterating 10 times to create 10 inner lists.
What is the significance of adding an incrementer in the while loop?
-The incrementer ensures that the while loop progresses and eventually terminates, preventing an infinite loop from occurring.

Outlines

00:00

🎬 Introduction to Creating a Nested List in Python

The video begins with an introduction by Nikhil, welcoming viewers to learn about creating a nested list in Python. He explains that although using arrays would be easier when studying them later, the focus will be on lists for now. Nikhil hints at the use of 'for' and 'while' loops, and user-defined functions to achieve this goal. The objective is to generate ten lists, each containing values from 0 to 9, and nest them within a larger list.

05:01

🔧 Defining a Function to Generate a Single List

Nikhil explains how to define a function that creates a list of numbers from 0 to 9. He walks through the steps, starting with defining an empty list, followed by a 'for' loop that appends values from 0 to 9 into the list. The function is simple and does not require any arguments. Nikhil emphasizes the use of a docstring to document the function, which generates and returns a list with values 0 to 9. After running the function, the expected output—a list of numbers from 0 to 9—is displayed.

🔄 Attempting a While Loop for Nested Lists

Nikhil shifts to using a 'while' loop to create a nested list. He initializes the value 'i' and discusses how the loop will run as long as 'i' is less than 10, incrementing by 1 each time. The final objective is to create a 'nest_list', which is an empty list that will store the nested lists. He suggests using the previously defined 'listnum' function to generate the inner lists and then discusses different methods of adding the lists into 'nest_list', such as the 'extend' method.

🚫 Correcting the Extend Method Mistake

Nikhil runs into an issue when using the 'extend' method to add lists. Instead of creating nested lists, the values from the second list get added directly after the first list. He explains that 'extend' simply adds elements to the existing list, which is not what was intended. To fix this, he suggests switching to the 'append' method, which correctly adds each list as a separate element within the 'nest_list', thus forming the desired 10x10 nested list. Nikhil concludes by showcasing the correct nested list output.

Mindmap

Keywords

💡Nested list

A nested list refers to a list that contains other lists as its elements. In the video, the speaker discusses how to create a nested list in Python, which involves putting multiple lists (each containing values 0 to 9) inside a larger list. This is essential for understanding how data structures work when dealing with lists within lists.

💡Function

A function in Python is a block of reusable code designed to perform a specific task. In the video, the speaker creates a function to generate a list with numbers 0 to 9. This function is used to create multiple lists, which are later combined into a nested list. The explanation of how functions work is central to understanding modular programming.

💡For loop

A 'for loop' in Python is a control flow statement used to iterate over a sequence of values. In the video, the for loop is used to populate a list with values from 0 to 9. The loop ensures that the values are added to the list one by one, making it a key element in automating repetitive tasks.

💡While loop

A 'while loop' in Python repeatedly executes a block of code as long as a given condition is true. In the video, the speaker briefly mentions using a while loop to iterate through values while appending lists, but emphasizes the need for an incrementer to avoid an infinite loop. This shows how control flow structures work in programming.

💡Append

The 'append' method in Python adds a single item to the end of a list. In the video, 'append' is used to add each new list (with values 0 to 9) into the larger nested list. This is in contrast to the 'extend' method, which the speaker also mentions, illustrating the difference between adding elements versus adding whole lists.

💡Extend

'Extend' is a method in Python used to add all elements of an iterable (like a list) to the end of a list. The video shows that using 'extend' instead of 'append' would flatten the lists into a single list, rather than creating a nested list. This highlights how different methods affect the structure of lists.

💡Range

'Range' is a built-in Python function that generates a sequence of numbers. In the video, the speaker uses 'range(0, 10)' to generate numbers from 0 to 9, which are then added to the list. This function is frequently used in loops to specify the number of iterations.

💡List

A 'list' is a mutable data structure in Python that holds an ordered collection of items. The video focuses on creating lists of numbers from 0 to 9 and then combining them into a nested list. Understanding how lists operate is fundamental to manipulating and organizing data in Python.

💡Empty list

An empty list is a list that contains no elements. In the video, the speaker starts by initializing an empty list to which elements (numbers 0 to 9) are appended. Empty lists are often used as placeholders to store data generated later in the program.

💡User-defined function

A 'user-defined function' is a function created by the programmer to perform specific tasks, rather than relying on built-in functions. The video emphasizes defining a function to generate a list with numbers 0 to 9. By using this user-defined function, the speaker demonstrates how to encapsulate code for repeated use.

Highlights

Introduction to creating a nested list in Python using basic functionalities like for loops, while loops, and user-defined functions.

Importance of understanding arrays and how lists serve as a Python substitute when working within its constraints.

Explanation of how to generate a list with values from 0 to 9 using a simple Python function.

Defining a function without any arguments to return a list from 0 to 9.

Detailed breakdown of how to use a for loop to append values to the list.

Creating a single list of 10 values (from 0 to 9) through a function and understanding list generation in Python.

The role of the return statement in functions to return the newly generated list.

Using a while loop for list creation and ensuring loop control with an incrementer to avoid infinite loops.

Introduction to using the extend() function and its impact when incorrectly trying to create nested lists.

Understanding the difference between extend() and append() when working with lists.

Explanation of how extend() adds elements to the original list instead of creating a new nested list.

Switching to append() to correctly generate a nested list with 10 rows and 10 columns.

Using append() to create a list of lists where each element is itself a list.

Final result: A nested list with 10 lists, each containing values from 0 to 9.

Conclusion and validation of the code to ensure it generates the desired nested list structure.