What does Python treat as reference types?

python sequences value-type reference-type
Hubro picture Hubro · May 28, 2011 · Viewed 11.9k times · Source

I assumed sequence types in Python were value types. It turns out they're reference types (Meaning that the value of a variable won't be copied when assigned to a new variable, but referenced). So now I'm wondering, what are the value types in Python? That is, what types in Python can I assign to new variables without worrying that the variable was referenced?

Answer

Ignacio Vazquez-Abrams picture Ignacio Vazquez-Abrams · May 28, 2011

All values in Python are references. What you need to worry about is if a type is mutable. The basic numeric and string types, as well as tuple and frozenset are immutable; names that are bound to an object of one of those types can only be rebound, not mutated.

>>> t = 1, 2, 3
>>> t[1] = 42
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment

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