I was reading the reference implementation of PEP-661: Sentinel Values and discovered an optimization technique known as String interning. Modern programming languages like Java, Python, PHP, Ruby, Julia, etc, performs string interning to make their string operations more performant.
String interning
String interning makes common string processing operations time and space-efficient by caching them. Instead of creating a new copy of string every time, this optimization method dictates to keep just one copy of string for every appropriate immutable distinct value and use the pointer reference wherever referred.