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Why are strings made immutable by default in some langs (I have seen this mainly in java and python)? Nothing fundamentally requires strings to be so. Has some analysis been done indicating most string operations in software would benefit by immutable form rather than non-immutable form?

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At least in Python, string objects are widely used as keys to dictionaries or as options in functions. For speed and efficiency these small strings are "interned" so that there is only ever one instance of the same string.

Also for mutable strings you either have to allocate enough memory to fit the final result or have some kind of rope data structure. Or else you end up copying it anyway.

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