Immutable Types Can’t Be Changed In-Place

You can’t change an immutable object in-place. Instead, you construct a new object with slicing, concatenation, and so on, and assign it back to the original reference, if needed:

T = (1, 2, 3)

T[2] = 4              # Error!

T = T[:2] + (4,)      # OK: (1, 2, 4)

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That might seem like extra coding work, but the upside is that the previous gotchas can’t happen when you’re using immutable objects such as tuples and strings; because they can’t be changed in-place, they are not open to the sorts of side effects that lists are.