foo = "bar"
foo[0] = "c" # Error 

Immutable variable value can not be changed once they are created.

foo = ("bar", 1, "Hello!",)
foo[1] = 2 # ERROR!! 

Second line would return an error since tuple members once created aren't assignable. Because of tuple's immutability.

foo = frozenset(["bar", 1, "Hello!"])
foo[2] = 7 # ERROR
foo.add(3) # ERROR

Second line would return an error since frozenset members once created aren't assignable. Third line would return error as frozensets do not support functions that can manipulate members.