Python Set `discard()` Method

set.discard() removes one item from a set.

Use it when you want to remove a value safely, even if that value might not be in the set. Unlike set.remove(), discard() does not raise an error for a missing item.

Quick example

colors = {"red", "blue", "green"}
colors.discard("blue")
print(colors)

colors.discard("yellow")  # no error if missing
print(colors)

Possible output:

{'red', 'green'}
{'red', 'green'}

Use discard() when you want to remove a value from a set safely, even if that value may not exist.

What `set.discard()` does

discard():

Removes one item from a set
Does nothing if the item is not in the set
Changes the original set in place
Returns None

This means the set itself is updated. Python does not create a new set.

If you are new to sets, see what a set is in Python or how to create a set.

Basic syntax

my_set.discard(value)

my_set is the set you want to change
value is the item you want to remove
The set must already exist
The value must be a valid set element type

Example

numbers = {1, 2, 3, 4}
numbers.discard(3)
print(numbers)

Output:

{1, 2, 4}

What makes `discard()` different

discard() is similar to other set methods, but it behaves differently in an important way.

Unlike remove(), discard() does not raise KeyError when the item is missing
Unlike pop(), discard() removes a specific item
It is useful when you are not sure whether the item exists

`discard()` vs `remove()`

items = {"apple", "banana"}

items.discard("orange")   # no error
print(items)

items.remove("banana")    # removes existing item
print(items)

Output:

{'apple', 'banana'}
{'apple'}

If you call remove() with a missing value, Python raises an error. See KeyError in Python for more help with that case.

What the method returns

discard() returns None.

That means you should not write code like this:

colors = {"red", "blue", "green"}
result = colors.discard("blue")

print(result)

Output:

None

The changed set is still stored in colors:

colors = {"red", "blue", "green"}
colors.discard("blue")

print(colors)

Output:

{'red', 'green'}

Simple example

Here is a basic example that removes an existing item.

fruits = {"apple", "banana", "orange"}

print("Before:", fruits)

fruits.discard("banana")

print("After:", fruits)

Output:

Before: {'banana', 'apple', 'orange'}
After: {'apple', 'orange'}

The order of items in a set may look different on your computer because sets are unordered.

Example with a missing item

One of the most useful features of discard() is that it does not fail if the item is missing.

fruits = {"apple", "banana", "orange"}

fruits.discard("grape")

print(fruits)

Output:

{'banana', 'apple', 'orange'}

No error happens here.

This is helpful in beginner code because you do not need to check first:

if "grape" in fruits:
    fruits.remove("grape")

With discard(), you can simply write:

fruits.discard("grape")

When to use `discard()`

Use discard() when:

Missing values are normal
You want simple, safe removal
You do not want to write an existence check first

It is a good choice when your program does not care whether the value was already missing.

Common mistakes

Here are some common beginner mistakes with discard().

Expecting `discard()` to return the changed set

This is wrong:

numbers = {1, 2, 3}
numbers = numbers.discard(2)

print(numbers)

numbers becomes None because discard() returns None.

Use this instead:

numbers = {1, 2, 3}
numbers.discard(2)

print(numbers)

Confusing `discard()` with `remove()`

If you want to avoid errors for missing values, use discard().

letters = {"a", "b", "c"}
letters.discard("z")   # safe
print(letters)

If you use remove("z"), Python raises a KeyError.

Trying to use `discard()` on a list instead of a set

discard() is a set method, not a list method.

Wrong:

items = [1, 2, 3]
items.discard(2)

Use a set if you need discard():

items = {1, 2, 3}
items.discard(2)
print(items)

Passing an unhashable value such as a list

Set items must be hashable. A list is not hashable.

This causes an error:

data = {1, 2, 3}
data.discard([2])

Use a valid set element type instead, such as a number, string, or tuple.

Helpful debugging checks

If discard() is not working as expected, these quick checks can help:

print(my_set)
print(type(my_set))
print(value in my_set)
help(set.discard)

These checks help you confirm:

What is currently in the set
Whether the variable is really a set
Whether the value exists before removal
How Python documents the method

FAQ

What happens if the item is not in the set?

Nothing happens. discard() does not raise an error when the item is missing.

What does `set.discard()` return?

It returns None. It changes the original set instead of creating a new one.

What is the difference between `discard()` and `remove()`?

Both remove items from a set. remove() raises KeyError if the item is missing, but discard() does not.

Can I use `discard()` with lists or dictionaries?

No. discard() is a set method, so it works on set objects.

Python Set discard() Method

Python Set `discard()` Method