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gh-95337: update TypeVarTuple example (#95338)
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
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@ -1305,20 +1305,25 @@ These are not used in annotations. They are building blocks for creating generic
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T = TypeVar('T')
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Ts = TypeVarTuple('Ts')
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def remove_first_element(tup: tuple[T, *Ts]) -> tuple[*Ts]:
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return tup[1:]
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def move_first_element_to_last(tup: tuple[T, *Ts]) -> tuple[*Ts, T]:
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return (*tup[1:], tup[0])
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# T is bound to int, Ts is bound to ()
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# Return value is (), which has type tuple[()]
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remove_first_element(tup=(1,))
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# Return value is (1,), which has type tuple[int]
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move_first_element_to_last(tup=(1,))
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# T is bound to int, Ts is bound to (str,)
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# Return value is ('spam',), which has type tuple[str]
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remove_first_element(tup=(1, 'spam'))
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# Return value is ('spam', 1), which has type tuple[str, int]
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move_first_element_to_last(tup=(1, 'spam'))
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# T is bound to int, Ts is bound to (str, float)
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# Return value is ('spam', 3.0), which has type tuple[str, float]
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remove_first_element(tup=(1, 'spam', 3.0))
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# Return value is ('spam', 3.0, 1), which has type tuple[str, float, int]
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move_first_element_to_last(tup=(1, 'spam', 3.0))
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# This fails to type check (and fails at runtime)
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# because tuple[()] is not compatible with tuple[T, *Ts]
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# (at least one element is required)
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move_first_element_to_last(tup=())
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Note the use of the unpacking operator ``*`` in ``tuple[T, *Ts]``.
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Conceptually, you can think of ``Ts`` as a tuple of type variables
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