Python Set symmetric_difference() Method

set.symmetric_difference() returns the values that appear in exactly one of two sets.

This is useful when you want to compare two sets and keep only the non-matching values.

Use it when:

• you want items in one set or the other
• you do not want items that appear in both sets
• you need a new set without changing the originals

Quick answer #

a = {1, 2, 3}
b = {3, 4, 5}

result = a.symmetric_difference(b)
print(result)  # {1, 2, 4, 5}

Use this when you want values that are in one set or the other, but not in both.

What symmetric_difference() does #

set.symmetric_difference():

• returns a new set
• keeps items that are in only one of the two sets
• removes items that exist in both sets
• does not change the original set

If you are new to sets, see Python sets explained or creating a set in Python.

Basic syntax #

set1.symmetric_difference(set2)

Notes:

• set1 must be a set
• set2 can be any iterable
• the result is always a set
• the most common use is comparing two sets

Example:

set1 = {1, 2, 3}
set2 = {3, 4, 5}

result = set1.symmetric_difference(set2)
print(result)

Output:

{1, 2, 4, 5}

What the result means #

The result includes:

• items only in the first set
• items only in the second set

The result does not include:

• items shared by both sets

For example:

• first set: {1, 2, 3}
• second set: {3, 4, 5}

The value 3 is in both sets, so it is removed from the result.

The output is:

{1, 2, 4, 5}

Also remember:

• sets are unordered
• Python does not guarantee the printed order of set items

Simple example #

Here is a small example with one shared value:

colors1 = {"red", "blue", "green"}
colors2 = {"green", "yellow"}

result = colors1.symmetric_difference(colors2)

print(result)

Output:

{'red', 'blue', 'yellow'}

What happened here:

• "green" is in both sets, so it is excluded
• "red" and "blue" are only in colors1, so they stay
• "yellow" is only in colors2, so it stays

symmetric_difference() vs difference() #

These two methods are similar, but they do not do the same thing.

difference():

• keeps items only from the first set
• ignores unique items from the second set

symmetric_difference():

• keeps unique items from both sets
• removes shared items

Example:

a = {1, 2, 3}
b = {3, 4, 5}

print(a.difference(b))            # {1, 2}
print(a.symmetric_difference(b))  # {1, 2, 4, 5}

Use:

• difference() for a one-sided comparison
• symmetric_difference() for a two-sided comparison

symmetric_difference() vs union() #

union() combines both sets.

symmetric_difference() only keeps non-shared values.

Example:

a = {1, 2, 3}
b = {3, 4, 5}

print(a.union(b))                 # {1, 2, 3, 4, 5}
print(a.symmetric_difference(b))  # {1, 2, 4, 5}

Difference:

• union() includes everything
• symmetric_difference() excludes values found in both sets

Use:

• union() when overlap does not matter
• symmetric_difference() when you want non-matching values only

Using the ^ operator #

For sets, the ^ operator gives the same result as symmetric_difference().

Example:

set1 = {1, 2, 3}
set2 = {3, 4, 5}

print(set1.symmetric_difference(set2))
print(set1 ^ set2)

Possible output:

{1, 2, 4, 5}
{1, 2, 4, 5}

Both forms:

• return a new set
• do not change the original sets

For beginners, the method form is often easier to read because the name explains what it does.

Common beginner mistakes #

Here are some common problems when using symmetric_difference():

• Expecting sorted output
  Sets are unordered, so the result may print in a different order than you expect.

• Thinking the original set is changed
  symmetric_difference() returns a new set. It does not modify the original set.

• Confusing it with difference()
difference() only keeps items from the first set. symmetric_difference() keeps unique items from both sets.

• Forgetting that sets remove duplicates
  A set only stores unique values. If your original data has repeated values, they will appear only once.

Common causes of confusion include:

• using symmetric_difference() when union() is actually needed
• comparing lists instead of converting them to sets first
• assuming repeated values will appear multiple times in the result
• being confused by output order

If you are starting with a list and want unique values first, see how to remove duplicates from a list in Python.

Useful checks while debugging:

print(set1)
print(set2)
print(set1.symmetric_difference(set2))
print(set1 ^ set2)
print(type(set1))
print(type(set2))

FAQ #

Does symmetric_difference() change the original set? #

No. It returns a new set and leaves the original set unchanged.

What is the difference between symmetric_difference() and difference()? #

difference() keeps items only from the first set. symmetric_difference() keeps items that appear in exactly one of the two sets.

Can I use symmetric_difference() with lists? #

The method is for sets. Convert a list to a set first if needed.

Example:

list1 = [1, 2, 3]
list2 = [3, 4, 5]

result = set(list1).symmetric_difference(set(list2))
print(result)

Output:

{1, 2, 4, 5}

Why does the output order look random? #

Sets are unordered, so Python does not guarantee item order.

See also #

• Python sets explained
• Creating a set in Python
• Python set difference() method
• Python set union() method
• How to remove duplicates from a list in Python

If you are learning set methods, compare difference(), union(), and symmetric_difference() side by side. That makes it much easier to choose the right one for real tasks.