How to remove an element from a list by index in Python？

To remove an element from a list by index in Python, you can use del or pop(), each with distinct behaviors. Below is a detailed guide with expanded examples, edge cases, and advanced techniques.

1. Using del Statement

The del keyword removes an element by index without returning its value. It directly modifies the original list.

Syntax:

del list_name[index]          # Remove single element
del list_name[start:end]      # Remove a slice (range)

Examples:

• Remove a single element:

  fruits = ["apple", "banana", "cherry", "date"]
  del fruits[1]  # Remove index 1 ("banana")
  print(fruits)  # Output: ["apple", "cherry", "date"]

• Remove a slice (range):

  numbers = [10, 20, 30, 40, 50]
  del numbers[1:3]  # Remove indices 1-2 (20, 30)
  print(numbers)    # Output: [10, 40, 50]

• Negative indices (access from the end):

  letters = ["a", "b", "c", "d"]
  del letters[-2]  # Remove the second-last element ("c")
  print(letters)    # Output: ["a", "b", "d"]

2. Using pop() Method

The pop() method removes an element by index and returns its value. If no index is specified, it removes the last element.

Syntax:

removed_value = list_name.pop()     # Remove last element
removed_value = list_name.pop(index) # Remove at specific index

Examples:

• Remove and return the last element:

  colors = ["red", "green", "blue"]
  removed = colors.pop()  # "blue" is removed
  print(colors)  # Output: ["red", "green"]
  print(removed) # Output: "blue"

• Remove and return a specific index:

  numbers = [100, 200, 300, 400]
  removed = numbers.pop(0)  # Remove index 0 (100)
  print(numbers)  # Output: [200, 300, 400]
  print(removed)  # Output: 100

3. Error Handling

Both methods raise an IndexError if the index is out of bounds. Use try-except to handle this gracefully.

Example:

my_list = [1, 2, 3]
try:
    del my_list[5]  # Invalid index
except IndexError as e:
    print(f"Error: {e}")  # Output: "list assignment index out of range"

4. Advanced Techniques

A. Remove Multiple Indices

To remove multiple indices without shifting issues, process indices in reverse order:

data = ["a", "b", "c", "d", "e"]
indices_to_remove = [0, 2, 4]  # Remove indices 0, 2, 4
for index in sorted(indices_to_remove, reverse=True):
    del data[index]
print(data)  # Output: ["b", "d"]

B. Immutable Removal (Create a New List)

Use a list comprehension to exclude specific indices:

original = [10, 20, 30, 40]
new_list = [val for idx, val in enumerate(original) if idx != 1]
print(new_list)  # Output: [10, 30, 40] (index 1 removed)

C. Avoid Modifying While Iterating

Modifying a list during iteration can cause unexpected behavior. Instead, iterate over a copy:

# ❌ Problematic approach:
numbers = [1, 2, 3, 4, 5]
for num in numbers:
    if num % 2 == 0:
        del numbers[numbers.index(num)]  # Risky!

# ✅ Safer approach:
for num in numbers.copy():
    if num % 2 == 0:
        numbers.remove(num)

5. Key Differences: del vs pop()

Feature	del	pop()
Return Value	None (no return)	Returns the removed element
Use Case	Remove elements permanently	Remove and use the value later
Flexibility	Can delete slices	Works with single indices

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6. Performance Considerations

• Both del and pop() have O(n) time complexity for arbitrary indices because elements after the removed index are shifted.
• To optimize, prefer pop(-1) (last element) which is O(1).

Summary

• Use del to permanently remove elements by index or slice.
• Use pop() to remove and retrieve the value.
• Handle IndexError for invalid indices.
• Process multiple indices in reverse order to avoid shifting issues.

This covers all major scenarios for removing elements by index in Python!