How can you find the difference between two sets in Python?
In Python, you can find the difference between two sets using the
.difference()
method. The
set
and
frozenset
objects contain a built-in method labelled
difference()
which helps to find the non-matching elements in the source object not found in the other sets passed in to the
.difference(*others)
parameter.
Here is an example demonstrating how to find the difference between two sets using the Python REPL:
>>> source_set = {10, 12, 14, 16, 18}
>>> other_set = {12, 16, 18}
>>> source_set.difference(other_set)
{10, 14}
As you can see from the above output the
source_set
is used as the baseline, and any corresponding elements that are found in the
other_set
are removed, leaving the result of
{10, 14}
.
Difference Between Multiple Sets
You can add more sets into the
.difference()
parameters if there are other sets to compare against.
For example, you could compare three sets and find which values remain in the
source_set
after comparing them against two other sets, as demonstrated below:
>>> source_set = {10, 12, 14, 16, 18}
>>> other_set = {12, 16, 18}
>>> third_set = {10}
>>> source_set.difference(other_set, third_set)
{14}
As you can see the
source_set
is compared against each of the sets in the
difference()
method. The result can never be
more
than what is in the original
source_set
.
What if you just wanted to update the
source_set
rather than produce a new set?
Remove Differences By Updating Source Set
What if you didn’t want to produce a new set but rather wanted to just update the
source_set
?
There is another method called
.difference_update(*others)
which enables this functionality.
Using the previous example above, here’s how this would look in the Python REPL:
>>> source_set = {10, 12, 14, 16, 18}
>>> other_set = {12, 14, 16}
>>> source_set.difference_update(other_set)
>>> source_set
{10, 14}
As you can see the method performs the necessary task of removing the shared elements from the
source_set
. If there are multiple sets to compare, you could wrap them all into one parameter as previously done with the
.difference(*others)
method.
Here’s how this would look applying multiple sets on the
source_set
:
>>> source_set = {10, 12, 14, 16, 18}
>>> other_set = {12, 16, 18}
>>> third_set = {10}
>>> source_set.difference_update(other_set, third_set)
>>> source_set
{14}
As you can see, this produces the same outcome and mutates the original
source_set
variable.
Summary
In Python, you can find the difference between two sets using the
.difference()
method. The
set
and
frozenset
objects contain a built-in method labelled
difference(*others)
which helps to find the non-matching elements in the source object not found in the other sets passed in to the
*others
parameter. You can add more sets into the
.difference()
method if there are other sets to compare against.
If you would prefer to update the original
source_set
being compared against rather than producing a new set, you could use another method called
.difference_update(*others)
.
