Python is an object-oriented programming language that provides rapid application development which was released in 1991 by Guido van Rossum. It has a huge demand in Rapid Application Development due to its dynamic binding and typing options. Some features of Python, which make it the most popular programming language right now is that it is free and open-source, has a vast standard library, and it can be integrated with other programming languages easily.
What is Python?
Python is a general-purpose programming language that is often applied to scripting roles. Scripting languages tend to be limiting, but Python, on the other hand, is an uncomplicated and robust programming language that delivers both the power and complexity of traditional style. Python is designed to be very efficient in writing and especially to read.
Features of Python
Some of the most significant features of PythonPython are:
- Accessible to Code: Python is a highly user-friendly programming language, allowing for quick and easy comprehension for developers. Compared to other object-oriented languages such as Java, C, C++, and C#, Python is relatively simple to understand.
- Open Source and Free: Python is an open source programming language anyone can create and contribute to its development. Also, Python is free for downloading and use in any operating system like Windows, Mac, or Linux.
- Support for GUI: GUI or Graphical User Interface is one of the critical aspects of any programming language because it can add flair to code and make the results more visual. Python supports many arrays of GUIs, which are easy to import to the interpreter, making it one of the most favorite languages for developers.
- High-Level Language: Python is designed to be a high-level programming language. When you code in Python, you don't need to be bothered by the coding structure, architecture, and memory management.
- Extensive Array of Library: Python has enormous inbuilt libraries that can be imported anywhere and used in a specific program. The presence of libraries also ensures that you can import the same from those existing in the libraries.
- Highly Portable: Suppose you are running Python on Windows and need to shift the same to either a Mac or a Linux system. You can quickly achieve the same in Python without changing the code. This cannot be done in other programming languages, so Python is the most portable language available in the industry.
Introduction to Python List
A Python list is a collection of zero or more elements. An element of the list can be any data. It can be string, numerical, or a combination of both types. A list in Python is like an array in C or Java. Lists are mutable- that is, you can change their content-and they have many useful specialized methods.
How to Create a Python List?
A Python list is created by adding elements in the square brackets [ ].
num = [1, 2, 3, 4]
letter = [‘a’, ‘b’, ‘c’, ‘d’]
Fig: Create the Python List
These lists can contain elements of different types.
Creating a Python List
A list is created in PythonPython by placing items inside , separated by commas. A list can have any number of things; they can be of different types (integer, float, string, etc.).
- Access in Python list: Each item in a list is related to a number. The number is known as the list index. It accesses elements of an array using the index number (0, 1, 2, 3 …).
- Negative Indexing in PythonPython: Python allows negative indexing for sequences. If the specified index does not, it shows the "Index Error" exception.
- Slicing in Python list: In Python, it is possible to access a section of items from the List using the slicing operator ":" not just a single item.
Just note that when we slice lists, the start index is inclusive, but the end index is exclusive.
Access Elements From List
Every Python list starts with the index ‘0’. We can access the elements by specifying the index number. For example: To access elements in the list, we provide the index (as integer) inside the square brackets ( [ ] ) as given below.
Fig: Access elements from starting of the list
To access the elements from the end we use negative indexing. -1 means the last element. -2 the second last element and so on. For instance, if you want to access the 4th element from the ending of the list named mix, you write mix[-4].
Fig: Access the elements from ending of the list
You can also access the elements from a specific range. To get elements from index 1 to index 3 from the list mix, you should write mix[1:4].
Fig: Access the elements from a specific range
Remember that the first item is position 0.
Note: The search will start at index 1 (included) and end at index 4 (not included)
If the starting value is left out, the range will begin from the starting element. For instance:
Fig: Get elements from Index 0
Change and Add Elements to the List
In a Python list, the element value can be changed by specifying the index number and replacing it with a new value. For instance:
Fig: To change the element in Python List
For adding new elements to a list in Python, you can use the ‘append ()’ method or ‘insert ()’ method.
1. Using the Append() Method
The append() method adds the element to the end of the list. For example:
Fig: Adding element by using append () method
2. Using the Insert() Method
If you want to insert an element at a specific index, you should use the insert () method.
Fig: Add element using insert() method
Delete Elements From a List
There are two ways of removing elements from a list:
1. Delete Specified Elements We Use Remove() Method.
Suppose you want to delete the item “get” from the list “mix”. We write it as mix.remove(“get”).
Fig: To delete element by using remove()
2. To Remove the Element From Specific Index We Use Del() Method
Syntax: del list_name [index]
Fig: Deleting element using the del() method
Check if the Item Exists in List
You can check if the particular element exists in the list or not. The following example can be used to perform the same:
Fig: Check if the item exists in the list
Check the Length of the List
You can check the number of items in the list by using ‘len ()’ method
Fig: To check the number of items in the list
To Join the Two List
There are several ways to join two lists, and the easiest method is to use the ‘ + ‘ operator. This can be done in the following way:
Fig: Join two Python lists
Updating List in Python
There are different ways to update a Python list, and we can use any of them for updation. The Python list offers various methods for altering data.
- List.append (value) Append a value: If you like to add a single element to the python list, then List.append(value) is the best fit for you. The List.append(value) always adds the value to the end of the existing List.
- List.extend(iterable) Append a series of values: The append and extend methods have a similar purpose of adding data at the end of a list. The contrast lies in the fact that the append method incorporates a solitary element to the conclusion of the List. In contrast, the extend method appends a series of elements from a collection or iterable.
- List.insert(index, value) At index, insert value: The insert() method is similar to the append() method; however, the insert method inserts the value at the given index position, whereas append() always adds the element at the end of the List.
- List.remove(value) Remove the first instance of value: The remove(value) method removes the first occurrence of the given value from the List. There must be one occurrence of the provided value; otherwise, the PythonPython raises ValueError.
- List.clear() # Remove all elements: The clear() method is used to remove all the elements from the List. We can also perform the same action with del List [:] in a similar manner.
List Items in Python
List items are of different types; those can be ordered, changeable and allow duplicate values.
- Ordered List: When the List is ordered, the items are in a defined order, and the order doesn't change if new items are added to the List; the new items are placed at the end. Note: Some list methods will change the order, but generally, the order of the items will not change.
Changeable: The lists are changeable, meaning we can either change, add, or remove items in a list after it has been created. Allow Duplicates-Since lists are indexed in Python, lists can have items with the same value.
List Items: Data Types: List items are of any data type like string, int or boolean, etc.
- Type(): Lists are defined as objects with the data type 'list'; text added with this type will be considered a list in PythonPython.
- The List() Constructor: It is possible to use the List () constructor when we create a new list; any data type can be used for creating a list with it.
- Python Collections (Arrays): There are four collection data types in the PythonPython as follows :
- List: A List is a type of collection that is arranged in a specific order and can be modified. Additionally, it permits the inclusion of duplicate items.
- Tuple: A tuple is an ordered and immutable collection of elements.
- Set: is an unordered, unchangeable*, and an unindexed collection. No duplicate members.
- Dictionary: is a collection that is ordered** and changeable. There are no duplicate members.
Iterating a List in Python
There are six ways with which we can iterate a list in PythonPython.
- Using Loop: The easiest way to iterate Lists in programming is by using them for a loop.
- Using Loop and Range() Function: This method to iterate the List while programming uses the loop and range() function together. Iterating the List utilizing this method is not recommended if iteration using a for loop is possible.
- Using While Loop: we can also iterate the List in PythonPython using a while loop.
- Using List Comprehension: This is the most robust method for iterating the List while programming in Python.
- Using Enumerate() Function: You may need to display the element's index and the element in the List itself a few times. We use the enumerate() function for the List iteration in such cases.
- Using Numpy Function: Methods that have been discussed till now are preferable for small or single-dimensional lists. But n-dimensional lists are advised to use an external library like Numpy for iterating lists.
FOR and IN Loops in Python
A FOR loop is used for iterating in a sequence (a list, a tuple, a dictionary, a set, or a string); it's not like FOR keyword in other programming languages and acts like an iterator method, as found in other object-oriented languages. With FOR loop, we can execute a set of statements once in a list, tuple, set, etc. FOR loop does not require indexing variables to assess beforehand.
- Looping through String: strings are iterable objects containing a sequence of characters.
- The Break Statement: Break statement stops the loop before it has looped throughout all the items.
- The Continue Statement: Continue statement stops the current iteration of loop and continues with the next.
- The Range Function: Looping through a set of code specified number of times, we can use the Range() function; it gives a series of numbers that starts from 0, increments by 1, and ends at a specified number. Range() function gives 0 as a starting value. RANGE(2,6) means values from 2 to 6 but not 6.
- Else IN FOR Loop: The Else keyword in a FOR loop specifies a code block executed when the loop is finished.
- Nested Loop: It is a loop inside a loop element. The "inner loop" can be executed once for each iteration of the "outer loop."
- The Pass Statements: FOR loops cannot be empty, but for some reason, have a FOR loop with no content; put in the Pass statement to avoid getting an error.
Python List Comprehension
- List Comprehension: List comprehension gives a shorter syntax when we want to create a new list for the values of an existing list.
- The Syntax: The return value is a new list, leaving the old List unchanged.
- The Condition: The condition is like a filter that only accepts the items evaluated as TRUE and is optional.
- Iterable: An iterable is any object that can be iterated over, such as a list, tuple, or set.
- Expression: The expression is the current item in the iteration, but it is the outcome, which can be manipulated before it ends up like a list item in the new List.
Taking Input from a Python List
To accept input from the user in PythonPython, we can use the input() function. When used, it enables the programmer to get a string, integer, or even a character as input from the user. But the approach we follow is slightly different when accepting a list as input.
Complexities for Various Functions and Elements in List
For all the data consumed and generated every day, algorithms should be good enough to handle operations in large volumes of data.
- Computational Complexity: Computational complexity is a field of computer science that analyzes algorithms based on the number of resources required to run them. The amount of necessary resources based on the input size and complexity is expressed as a function of n, where n is the input size.
- Time Complexity: When analyzing the time complexity of an algorithm, there can be three cases: best-case, average-case, and worst-case.
- Best Case: It solves the problem for best input.
- Average Case: This is the average complexity of solving the problem.
- Worst Case: The complexity of solving problems for the worst input of size n.
- Big-O Notations: Big-O notation, also called "asymptotic notation," is a mathematical notation that signifies the limiting behavior of any function when the argument goes towards a particular value or infinity.
Reversing a List in Python
Various built-in functions are available to reverse a list in PythonPython. But choosing which to use for the specific problem needs to be clarified.
- Using Reverse() Method: There is an in-built method known as Reverse() in Python, which can reverse the List by changing elements in the original List. This method can be used in conditions where memory efficiency is required.
- Using Reversed() Method: This is a built-in function to reverse list elements without creating copies or modifying the original List. It also creates an iterator and stores the details.
- Using Slicing Operation: A slicing operation is performed to access the list elements from a starting-to-end index. The slicing operation can help reverse the List in Python.
- Using Recursion: The List can be reversed by recursion without built-in functions. Recursion means calling the function again and again.
Built-in Functions In Python List
Python consists of some in-built functions that we can use.
Removes all the elements from the list
Returns a copy of the list
Adds an element to the end of the list
Add an element to the specified position
Removes the element from the specified position
Removes the item with the specified value
Reverses the order of the list
Returns the number of elements with the specified value
Returns the index of an element in the list
Here are some examples of the functions that are mentioned in the table:
The clear() function removes all the elements from the list.
Fig: Clear a Python list
The copy() function returns a copy of all the items in a list.
Syntax: new_list = mix.copy()
Fig: Copy one Python list to another list
The reverse method prints the items in a list in the reverse order.
Fig: Reverse a Python List
The index method returns the index of the specified item in a list.
Fig: Find the index in a list
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