Glossary

9.1 Modifying and iterating lists

3 min read•june 24, 2024

Lists in Python are versatile data structures that allow for easy modification and . They're mutable, meaning you can change their contents after creation, and offer various methods for adding, removing, and accessing elements.

Iterating through lists is a fundamental skill in Python programming. Whether using for loops, list comprehensions, or built-in functions, mastering list iteration techniques enables efficient data manipulation and analysis in your code.

List Modification and Iteration

List modification operations

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  • ###[append](https://www.fiveableKeyTerm:append)()_0###
    adds an element to the end of a list
    • Syntax: 
      list_name.append(element)
    • Appends the specified element to the end of the list (
      numbers.append(10)
      adds 
      10
      to the end of the 
      numbers
      list)
  • [remove()](https://www.fiveableKeyTerm:remove())
    removes the first occurrence of a specified element from a list
    • Syntax: 
      list_name.remove(element)
    • Removes the first occurrence of the specified element from the list (
      fruits.remove("apple")
      removes the first occurrence of 
      "apple"
      from the 
      fruits
      list)
    • Raises a 
      ValueError
      if the element is not found in the list
  • [pop()](https://www.fiveableKeyTerm:pop())
    removes an element at a specified and returns its value
    • Syntax: 
      list_name.pop(index)
    • Removes the element at the specified index from the list and returns its value (
      numbers.pop(2)
      removes the element at index 
      2
      from the 
      numbers
      list and returns its value)
    • If no index is provided, 
      pop()
      removes and returns the last element in the list
  • Lists are mutable, allowing for of their elements

Iteration through lists

  • for
    loops iterate through each element in a list
    • Syntax: 
      for element in list_name:
    • Iterates through each element in the specified list (
      for fruit in fruits:
      iterates through each element in the 
      fruits
      list)
  • Access list elements using their indexes
    • List indexes start at 
      0
      for the first element and increment by 
      1
      for each subsequent element
    • Syntax: 
      list_name[index]
    • Accesses the element at the specified index in the list (
      fruits[0]
      accesses the first element in the 
      fruits
      list)
  • range()
    function with 
    [len()](https://www.fiveableKeyTerm:len())
    iterates through list indexes
    • Syntax: 
      for i in range(len(list_name)):
    • Iterates through the indexes of the specified list (
      for i in range(len(numbers)):
      iterates through the indexes of the 
      numbers
      list)

List comprehensions for creation

  • List comprehensions create new lists based on existing lists concisely
  • Syntax: 
    new_list = [expression for element in list_name if condition]
    • expression
      is the operation performed on each element
    • element
      is the variable representing each element in the original list
    • list_name
      is the name of the original list
    • if condition
      is an optional filter to include elements based on a condition
  • Create a new list with each element from the original list squared (
    squared_numbers = [x ** 2 for x in numbers]
    creates a new list with each element from 
    numbers
    squared)
  • Create a new list with only even numbers from the original list (
    even_numbers = [x for x in numbers if x % 2 == 0]
    creates a new list with only even numbers from 
    numbers
    )

Advanced List Operations

  • allows for extracting a portion of a list using a start index, end index, and optional step
  • The 
    in
    operator can be used to check for the presence of an element in a list during iteration
  • Iteration can be performed using various methods, including 
    for
    loops, list comprehensions, and built-in functions like 
    map()
    and 
    filter()

Key Terms to Review (11)

Append: The append method in Python adds a single element to the end of an existing list. It modifies the original list and does not return a new list.
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.
In-Place Modification: In-place modification refers to the ability to alter the contents of a data structure, such as a list, directly without creating a new copy. This allows for efficient memory usage and avoids the need to allocate additional storage space.
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.
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 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.
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.
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.
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