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gh-92877: Advise to use typing.IO sparingly #92878

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gh-92877: Advise to use typing.IO sparingly #92878

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Advise to use typing.IO sparingly
srittau May 17, 2022
4a5a9a4
Use standard positional-only syntax.
srittau May 17, 2022
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19 changes: 19 additions & 0 deletions Doc/library/typing.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -1940,6 +1940,25 @@ Other concrete types
represent the types of I/O streams such as returned by
:func:`open`.

These types should be used sparingly. For argument types, a tight
:class:`Protocol` that documents the actual needs of the implementation
is often a better alternative. Return values should be annotated with
the actual concrete type returned. For example::

from io import StringIO

class Reader(Protocol):
def read(self, size: int, /) -> bytes: ...
def close(self) -> object: ...

def to_text_stream(stream: Reader) -> StringIO:
s_io = StringIO()
while b := stream.read(1000):
s_io.write(b.decode("ascii"))
stream.close()
s_io.seek(0)
return s_io

.. deprecated-removed:: 3.8 3.12
The ``typing.io`` namespace is deprecated and will be removed.
These types should be directly imported from ``typing`` instead.
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