3.4 List basics
3 min read•june 24, 2024
Lists Python are versatile and powerful. They allow you to store and manipulate collections of data easily. You can access, modify, and perform operations on elements using simple syntax and built-in methods.
List manipulation is a key skill in Python programming. Understanding operations like , , and methods like and will help you work efficiently with lists. These tools give you flexibility in managing data structures.
List Fundamentals
List element access and modification
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- Lists are ordered collections of elements enclosed in [] (my_list = [1, 2, 3])
- Each element in a list is assigned a unique starting from 0 for the first element
- Access an element using the list name followed by the index in square brackets: list_name[index]
- my_list[0] returns 1
- Modify an element by assigning a new value to the specific index: list_name[index] = new_value
- my_list[1] = 4 changes the second element to 4 resulting in [1, 4, 3]
- access elements from the end of the list
- my_list[-1] returns the last element 3
- Lists are a type of , allowing for over their elements
Determining list length
- The function determines the number of elements in a list
- Takes the list as an argument and returns an integer representing the length
- Syntax: len(list_name)
- len(my_list) returns 3 if my_list = [1, 2, 3]
Mutability of Python lists
- Lists in Python are mutable meaning their elements can be changed after the list is created
- Modify add or remove elements from a list without creating a new object
- Different from immutable data types like strings or tuples where any changes create a new object
- Modifying list elements:
- Change the value of an element using its index: my_list[1] = 4
- Add elements using methods like append() or : my_list.append(5)
- Remove elements using methods like remove() or : my_list.remove(2)
- Be cautious of when working with mutable objects like lists
List Manipulation
Operations for list manipulation
- Lists support various operations and have built-in methods for manipulation
- Concatenation: Combine two lists using the + operator
- [1, 2] + [3, 4] results in [1, 2, 3, 4]
- : Multiply a list by an integer to repeat its elements
- [1, 2] * 3 results in [1, 2, 1, 2, 1, 2]
- Slicing: Extract a portion of a list using the slicing syntax list_name[start:end:step]
- my_list[1:4] returns a new list with elements from index 1 to 3
- append(): Add an element to the end of the list
- my_list.append(5) adds 5 to the end of the list
- insert(): Insert an element at a specific index
- my_list.insert(1, 6) inserts 6 at index 1
- remove(): Remove the first occurrence of a specified element
- my_list.remove(2) removes the first occurrence of 2 from the list
- pop(): Remove and return the element at a specified index (default: last element)
- my_list.pop() removes and returns the last element
- : Sort the elements of the list in ascending order
- my_list.sort() sorts the list in place
- : Reverse the order of the elements in the list
- my_list.reverse() reverses the order of the elements in place
- Lists can contain other lists, creating for more complex data structures
Advanced List Concepts
- : A concise way to create lists based on existing lists or other iterables
- : Creating a new list that references the same objects as the original list
- : Creating a new list with new objects that have the same values as the original list
Key Terms to Review (26)
Aliasing: Aliasing refers to the phenomenon where a digital signal is incorrectly represented due to an insufficient sampling rate, leading to the appearance of false or distorted frequencies in the reconstructed signal. This concept is particularly relevant in the context of list basics in Python.
Append(): The `append()` method is a built-in Python function that adds an element to the end of a list. This method is crucial for dynamically modifying lists, allowing you to grow your list as needed without defining its size beforehand. It not only supports basic operations on single-dimensional lists but also plays a significant role when working with nested structures and in data science for managing collections of data effectively.
Concatenation: Concatenation is the operation of joining two or more strings end-to-end to create a single string. This process is a fundamental aspect of working with text in programming, as it allows for dynamic string creation, manipulation, and formatting. Understanding concatenation is essential for tasks involving user input, data display, and creating readable outputs in code.
Deep Copy: A deep copy is a way of duplicating an object or data structure in programming, where the new copy is entirely independent of the original. This means that any changes made to the copy will not affect the original, and vice versa.
Escape sequence: An escape sequence is a series of characters used to represent special characters in a string. It typically begins with a backslash followed by one or more characters.
In: The term 'in' is a preposition that is used to indicate location, time, or inclusion within a specific context. It is a fundamental part of the English language and plays a crucial role in various programming concepts, including string manipulation, list operations, dictionary usage, and control flow structures.
Index: An index is a numerical or alphabetical reference point that allows for efficient access to specific elements within a larger data structure, such as a list or array. It serves as a way to uniquely identify and locate individual items within a collection.
Insert(): The insert() method is a built-in function in Python that allows you to add an element to a specific position within a list. It is a fundamental operation in working with lists, as it enables you to dynamically modify the contents of a list by inserting new elements at desired locations.
Iteration: Iteration is the process of repeating a set of instructions or operations multiple times in a computer program or algorithm. It is a fundamental concept in programming that allows for the execution of a block of code repeatedly until a specific condition is met.
Len(): The len() function is a built-in function in Python that returns the length or count of elements in a given object, such as a string, list, tuple, or dictionary. It is a fundamental operation that is widely used across various programming topics in Python.
List: A list in Python is an ordered collection of items, where each item can be of a different data type. Lists are one of the most fundamental and versatile data structures in the Python programming language, allowing you to store and manipulate multiple values in a single variable.
List comprehension: List comprehension is a concise way to create lists in Python using a single line of code. It consists of brackets containing an expression followed by a for clause and optionally, one or more if clauses.
List Comprehension: List comprehension is a concise and efficient way to create new lists in Python by applying a transformation or condition to each element of an existing list. It allows for the creation of lists in a single, compact expression, making code more readable and reducing the need for traditional looping structures.
Negative Indexes: Negative indexes in the context of list basics refer to the ability to access elements in a list by specifying a negative number as the index. This allows you to count backwards from the end of the list, providing an alternative way to reference the same elements.
Nested Lists: Nested lists are lists that are contained within other lists, creating a hierarchical structure. They allow for the organization of complex data by nesting different levels of information within a single list.
Not in: The 'not in' operator is a logical operator used to check if a value is not present in a sequence, such as a list, tuple, or string. It is the opposite of the 'in' operator, which checks if a value is present in a sequence.
Pop(): The pop() method is a fundamental operation in both lists and dictionaries in Python. It is used to remove and return an element from a specific position in a list or a key-value pair from a dictionary.
Remove(): The remove() method is a built-in function in Python that is used to remove a specific element from a list. It takes the element to be removed as an argument and permanently deletes it from the list.
Repetition: Repetition is the act of repeating or reiterating something, whether it's a word, phrase, action, or concept. In the context of Python's list basics, repetition is a fundamental programming technique used to manipulate and work with lists.
Reverse(): The reverse() method is a built-in function in Python that reverses the order of elements in a list. It modifies the original list, rather than creating a new one. This feature makes it a powerful tool for manipulating and rearranging data in the context of list basics and sorting/reversing lists.
Sequence: A sequence is an ordered arrangement of elements, such as numbers, letters, or objects, that follow a specific pattern or order. This concept is fundamental in various areas of computer science and mathematics, including programming, data structures, and algorithms.
Shallow Copy: A shallow copy is a type of object duplication in programming where the new object created points to the same memory locations as the original object. This means that changes made to the new object can affect the original object, and vice versa.
Slicing: Slicing is a fundamental operation in Python that allows you to extract a subset of elements from a sequence, such as a string, list, or other iterable data structures. It provides a powerful way to access and manipulate data by specifying the start, stop, and step of the desired subset.
Sort(): The sort() method is a built-in function in Python that allows you to rearrange the elements of a list in a specific order, either ascending or descending. It is a powerful tool for organizing and manipulating data stored in lists.
Sorting: Sorting is the process of arranging elements in a specific order, typically ascending or descending. In Python, lists can be sorted using built-in functions or custom sorting criteria.
Square Brackets: Square brackets, [], are a type of punctuation mark used to enclose additional information or to indicate a modification within a text. They are commonly employed in the context of lists and nested structures, serving as a way to organize and group related elements.