What is the difference between Python's list methods append and extend?

Difference Between Python's List Methods append and extend

In Python, lists have several methods for adding elements. Two commonly used methods are append and extend. Although they both add elements to a list, they operate differently. Understanding these differences is crucial for manipulating lists effectively.

append

The append method adds a single element to the end of the list. This element can be of any data type (another list, a number, a string, etc.).

Syntax:

list.append(element)

Example:

my_list = [1, 2, 3]
my_list.append(4)
print(my_list)  # Output: [1, 2, 3, 4]

# Appending a list
my_list.append([5, 6])
print(my_list)  # Output: [1, 2, 3, 4, [5, 6]]

extend

The extend method adds elements from an iterable (such as another list, a tuple, a set, etc.) to the end of the list. Unlike append, extend iterates over its argument and adds each element to the list.

Syntax:

list.extend(iterable)

Example:

my_list = [1, 2, 3]
my_list.extend([4, 5, 6])
print(my_list)  # Output: [1, 2, 3, 4, 5, 6]

# Extending with a string (iterable of characters)
my_list.extend('abc')
print(my_list)  # Output: [1, 2, 3, 4, 5, 6, 'a', 'b', 'c']

Key Differences

1. Functionality:

   • append adds its argument as a single element to the end of the list. The length of the list increases by one.
   • extend iterates over its argument, adding each element to the list. The length of the list increases by however many elements were in the iterable.

2. Type of Argument:

   • append can take any type of object as its argument.
   • extend requires an iterable (list, tuple, string, etc.) as its argument.

3. Resulting Structure:

   • append can result in a nested list if a list is appended.
   • extend always flattens the iterable into the list.

Example Comparison

Let's compare append and extend with an example to highlight their differences:

my_list = [1, 2, 3]

# Using append
my_list.append([4, 5])
print(my_list)  # Output: [1, 2, 3, [4, 5]]

# Resetting the list
my_list = [1, 2, 3]

# Using extend
my_list.extend([4, 5])
print(my_list)  # Output: [1, 2, 3, 4, 5]

Summary

• append:

  • Adds its argument as a single element to the end of the list.
  • Increases the list's length by one.
  • Argument can be any type of object.

• extend:

  • Iterates over its argument, adding each element to the list.
  • Increases the list's length by the number of elements in the iterable.
  • Requires an iterable (list, tuple, string, etc.) as its argument.

Understanding these differences helps in choosing the right method for adding elements to a list based on the desired outcome. For more detailed tutorials and practical examples on Python and other programming concepts, consider exploring Grokking the Coding Interview on DesignGurus.io, which provides comprehensive courses on essential coding and interview techniques.