Array Deletion at Beginning in DSA Python - Build from Scratch

Array Deletion at Beginning

📋 What You'll Learn

💡 Why This Matters

🌍 Real World

Managing daily tasks or to-do lists often requires removing completed tasks from the beginning to focus on the next ones.

💼 Career

Understanding how to manipulate lists by removing items is a basic skill useful in data processing, user interface updates, and many programming tasks.

1

Create the initial list of tasks

Create a list called tasks with these exact values in order: 'Wake up', 'Brush teeth', 'Eat breakfast', 'Go to work'

DSA Python

# Create the list called tasks with the given tasks
# Your code here

Hint

Use square brackets [] to create a list and separate items with commas.

2

Store the first task before deletion

Create a variable called first_task and set it to the first item in the tasks list

DSA Python

tasks = ['Wake up', 'Brush teeth', 'Eat breakfast', 'Go to work']
# Store the first task in first_task
# Your code here

Hint

Use tasks[0] to get the first item from the list.

3

Remove the first task from the list

Remove the first item from the tasks list using the del statement and index 0

DSA Python

tasks = ['Wake up', 'Brush teeth', 'Eat breakfast', 'Go to work']
first_task = tasks[0]
# Remove the first task from tasks
# Your code here

Hint

Use del tasks[0] to delete the first item from the list.

4

Print the updated list after deletion

Print the tasks list to show its state after removing the first task

DSA Python

tasks = ['Wake up', 'Brush teeth', 'Eat breakfast', 'Go to work']
first_task = tasks[0]
del tasks[0]
# Print the updated tasks list
# Your code here

Hint

Use print(tasks) to display the list.

Practice

1. What happens to an array when you delete the first element in Python using del arr[0]?

easy

A. The first element is removed and the rest shift left by one position.

B. The last element is removed instead of the first.

C. The array becomes empty regardless of its size.

D. The array remains unchanged.

Solution

1. Step 1: Understand del arr[0] operation

   This command removes the element at index 0, which is the first element of the array.

2. Step 2: Effect on the array

   After deletion, all elements after the first shift one position to the left to fill the gap.

3. Final Answer:

   The first element is removed and the rest shift left by one position. -> Option A

4. Quick Check:

   Deleting first element shifts others left [OK]

Hint: Deleting index 0 removes first element and shifts left [OK]

Common Mistakes:

• Thinking last element is removed
• Assuming array becomes empty
• Believing array stays the same

2. Which of the following is the correct syntax to delete the first element of a list named arr in Python?

easy

A. del arr(0)

B. del arr[0]

C. arr.delete(0)

D. arr.remove(0)

Solution

1. Step 1: Check Python syntax for deleting by index

   Python uses del arr[index] to delete element at a specific index.

2. Step 2: Analyze options

   del arr[0] uses correct syntax del arr[0]. del arr(0) uses parentheses which is invalid. arr.delete(0) uses a method that does not exist. arr.remove(0) removes by value, not index.

3. Final Answer:

   del arr[0] -> Option B

4. Quick Check:

   Use del with square brackets for index deletion [OK]

Hint: Use del with square brackets to delete by index [OK]

Common Mistakes:

• Using parentheses instead of square brackets
• Confusing remove() with delete by index
• Trying to call a non-existent delete() method

3. What is the output of the following code?

arr = [10, 20, 30, 40]
del arr[0]
print(arr)

medium

A. [20, 30, 40]

B. [10, 20, 30]

C. [30, 40]

D. [10, 20, 30, 40]

Solution

1. Step 1: Delete first element from array

   The command del arr[0] removes the element 10 at index 0.

2. Step 2: Remaining elements shift left

   After deletion, the array becomes [20, 30, 40].

3. Final Answer:

   [20, 30, 40] -> Option A

4. Quick Check:

   First element removed, rest shifted left [OK]

Hint: Deleting index 0 removes first element, print rest [OK]

Common Mistakes:

• Expecting first element to remain
• Confusing deletion with removing last element
• Printing original array without deletion

4. Find the error in the code below that tries to delete the first element of the list arr:

arr = [5, 10, 15]
arr.delete(0)
print(arr)

medium

A. The print statement is incorrect.

B. The index 0 is out of range.

C. The list is empty, so deletion fails.

D. The method delete() does not exist for lists.

Solution

1. Step 1: Check list methods for deletion

   Python lists do not have a method called delete(). Deletion by index uses del keyword or pop() method.

2. Step 2: Identify correct deletion method

   To delete first element, use del arr[0] or arr.pop(0). Using arr.delete(0) causes AttributeError.

3. Final Answer:

   The method delete() does not exist for lists. -> Option D

4. Quick Check:

   Use del or pop, not delete() [OK]

Hint: Lists have no delete() method; use del or pop [OK]

Common Mistakes:

• Using delete() method on list
• Assuming delete() works like in other languages
• Ignoring AttributeError from wrong method

5. You have an array arr = [1, 2, 3, 4, 5]. You want to delete the first element and then add 0 at the beginning. Which code correctly does this in Python?

hard

A. arr.remove(0)
arr.insert(0, 0)
print(arr)

B. arr.pop(0)
arr.append(0)
print(arr)

C. del arr[0]
arr.insert(0, 0)
print(arr)

D. del arr[1]
arr.insert(0, 0)
print(arr)

Solution

1. Step 1: Delete first element correctly

   Using del arr[0] removes the first element (1) from the array.

2. Step 2: Insert 0 at the beginning

   Using arr.insert(0, 0) adds 0 at index 0, shifting others right.

3. Step 3: Check other options

   arr.pop(0) arr.append(0) print(arr) appends 0 at the end, not beginning. arr.remove(0) arr.insert(0, 0) print(arr) tries to remove value 0 which is not in array. del arr[1] arr.insert(0, 0) print(arr) deletes second element, not first.

4. Final Answer:

   del arr[0] arr.insert(0, 0) print(arr) -> Option C

5. Quick Check:

   Delete first, then insert at start [OK]

Hint: Delete index 0, then insert new element at index 0 [OK]

Common Mistakes:

• Appending instead of inserting at start
• Removing value 0 instead of index 0
• Deleting wrong index