Strings cannot be modified in place. Understanding the implications changes how you reason about string-heavy code.
Python strings are immutable. This is stated in every introductory tutorial and genuinely understood by relatively few developers.
Immutability does not just mean "you cannot change a string." It means every string operation that appears to modify a string is actually creating a new string object. This has performance implications, mutation implications, and produces interview questions that trip up developers who have never thought carefully about what immutability means in practice.
The Illusion of Modification
s = "hello"
