List Methods — append(), insert(), remove(), pop(), clear()

What you will learn

Master the 5 most important list mutation methods: append(), insert(), remove(), pop(), and clear(). These methods modify the same list object in memory — the id() stays the same.

Method	Action
append()	Add one item at the end
insert()	Add at any index (+ve or −ve)
remove()	Delete first match by value
pop()	Delete by index and return the item
clear()	Remove all elements

Part of Collections lesson 2 · Review list basics: list data type.

Learning roadmap

Memory trick: Add → Insert → Remove → Pop → Clear

1. append() — add at the end

Syntax: listobj.append(value)

numbers = [10, 20]
numbers.append(30)
print(numbers)  # [10, 20, 30]

Remember:

• Always adds one item
• Adds to the last position
• Original list changes — same id()

Build from empty:

lst = []
lst.append(10)
lst.append(20)
lst.append(10)  # duplicates allowed
print(lst)  # [10, 20, 10]

2. insert() — add anywhere

Syntax: listobj.insert(index, value)

Positive index

Result

lst = [10, 20, 30, 40]
lst.insert(2, "RS")
print(lst)  # [10, 20, 'RS', 30, 40]

Negative index and edge cases

Code	Meaning
insert(-1, x)	Before last element
insert(0, x)	Beginning
insert(999, x)	Past end → same as append
insert(-400, x)	Before start → prepend

lst = [10, 20, 30, 40, 50]
lst.insert(-1, 155)   # before last
lst.insert(300, "HYD")    # invalid +ve → end
lst.insert(-400, "BANG")  # invalid −ve → start

3. remove() — delete by value

Syntax: listobj.remove(value)

lst = [10, 20, 10, 30]
lst.remove(10)
print(lst)  # [20, 10, 30]

Only the first 10 disappears. Raises ValueError if the value is missing.

Interview question: remove() works with values, not indexes.

4. pop() — delete by index

Two ways to use it

fruits = ["Apple", "Banana", "Orange"]
item = fruits.pop(1)
print(item)    # Banana
print(fruits)  # ['Apple', 'Orange']

last = fruits.pop()  # no arg → last item

Errors: IndexError on empty list or bad index.

Important difference

Method	Removes by	Returns
remove()	Value	None
pop()	Index	Removed item

5. clear() — empty the list

Syntax: listobj.clear()

lst = [10, 20, 30]
lst.clear()
print(lst)  # []

The list becomes empty, but it is still the same object in memory (id() unchanged). Returns None.

One-page comparison sheet

Method	Removes?	Returns	On missing / empty
append(v)	No	None	—
insert(i, v)	No	None	—
remove(v)	Yes (first)	None	ValueError
pop()	Yes (last)	value	IndexError
pop(i)	Yes (at i)	value	IndexError
clear()	All	None	safe on []

Mini project — student attendance system

attendance = ["Asha", "Ravi", "Meera"]

attendance.append("Kiran")      # late arrival
attendance.remove("Ravi")       # left early
attendance.insert(1, "Priya")   # new student

last = attendance.pop()         # undo last entry

print(attendance)
print(last)

Execution flow

This exercise combines append → remove → insert → pop, exactly like a real application.

Interview quick revision

Method	Use this when…	Example
append()	Add one item to end	Notifications queue
insert()	Place item at position	Priority queue
remove()	Delete known value	Remove username
pop()	Delete by index and get value	Undo feature
clear()	Reset everything	Logout / reset form

Practice questions

Test yourself before File 03 — Search and Extend:

1. What is the difference between append() and insert()?
2. Why does remove(10) delete only one value?
3. Which method returns the deleted element?
4. What happens if pop() is called on an empty list?
5. Does clear() create a new list object?

Knowledge check

Q1: lst = [1, 2, 3]; lst.append([4, 5]) — what is lst?
Answer: [1, 2, 3, [4, 5]] — one nested list appended as a single element.

Q2: Difference between remove(10) and pop(0)?
Answer: remove finds value 10; pop(0) removes whatever is at index 0.

Q3: Practice Q4 — pop() on []?
Answer: IndexError: pop from empty list.

Q4: Practice Q5 — does clear() create a new list?
Answer: No — same object, zero elements. id(lst) unchanged.