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PEP 597: Refinement (#1791)

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Inada Naoki 2021-01-31 12:44:30 +09:00 committed by GitHub
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@ -14,11 +14,11 @@ Abstract
========
Add a new warning category ``EncodingWarning``. It is emitted when
``encoding`` option is ommitted and the default encoding is locale
``encoding`` option is omitted and the default encoding is a locale
encoding.
The warning is disabled by default. New ``-X warn_encoding``
commandline option and ``PYTHONWARNENCODING`` environment variable
command-line option and ``PYTHONWARNENCODING`` environment variable
are used to enable the warnings.
@ -49,23 +49,24 @@ used actually. [2_]
Even Python experts assume that default encoding is UTF-8.
It creates bugs that happen only on Windows. See [3_] and [4_].
Raising a warning when the ``encoding`` option is omitted will
help to find such mistakes.
Emitting a warning when the ``encoding`` option is omitted will help
to find such mistakes.
Prepare to change the default encoding to UTF-8
-----------------------------------------------
We chose to use locale encoding for the default text encoding
in Python 3.0. But UTF-8 has been adopted very widely since then.
We had chosen to use locale encoding for the default text encoding in
Python 3.0. But UTF-8 has been adopted very widely since then.
We might change the default text encoding to UTF-8 in the future.
But this change will affect many applications and libraries.
Many ``DeprecationWarning`` will be raised if we start raising
the warning by default. It will be too noisy.
Many ``DeprecationWarning`` will be emitted if we start emitting the
warning by default. It will be too noisy.
While this PEP doesn't cover the change, this PEP will help to
reduce the number of ``DeprecationWarning`` in the future.
Although this PEP doesn't propose to change the default encoding,
this PEP will help to reduce the warning in the future if we decide
to change the default encoding.
Specification
@ -75,8 +76,8 @@ Specification
--------------------
Add new ``EncodingWarning`` warning class which is a subclass of
``Warning``. It is used to warn when ``encoding`` option is omitted
and the default encoding is locale-specific.
``Warning``. It is used to warn when the ``encoding`` option is
omitted and the default encoding is locale-specific.
Options to enable the warning
@ -86,11 +87,12 @@ Options to enable the warning
environment variable are added. They are used to enable the
``EncodingWarning``.
``sys.flags.encoding_warning`` is also added. It is a boolean flag
represents ``EncodingWarning`` is enabled.
``sys.flags.encoding_warning`` is also added. The flag represents
``EncodingWarning`` is enabled.
When the option is enabled, ``io.TextIOWrapper()``, ``open()``, and
other modules emit ``EncodingWarning`` when ``encoding`` is omitted.
other modules using them will emit ``EncodingWarning`` when
``encoding`` is omitted.
``encoding="locale"`` option
@ -120,7 +122,7 @@ supported too. For example,
-----------------------
``io.text_encoding()`` is a helper function for functions having
``encoding=None`` option and pass it to ``io.TextIOWrapper()`` or
``encoding=None`` option and passing it to ``io.TextIOWrapper()`` or
``open()``.
Pure Python implementation will be like this::
@ -155,17 +157,25 @@ For example, ``pathlib.Path.read_text()`` can use the function like:
with self.open(mode='r', encoding=encoding, errors=errors) as f:
return f.read()
By using ``io.text_encoding()``, ``EncodingWarning`` is emitted for
the caller of ``read_text()`` instead of ``read_text()``.
``subprocess`` module
----------------------
The default encoding for pipe in the subprocess module is changed
to ``io.LOCALE_ENCODING``. In other words, subprocess module doesn't
emit the ``EncodingWarning``.
Affected stdlibs
-------------------
The default encoding for PIPE is relating to the encoding of the
stdio than the default encoding of ``TextIOWrapper``. So this PEP
doesn't propose to emit the warning for pipes.
Many stdlibs will be affected by this change.
Most APIs accepting ``encoding=None`` will use ``io.text_encoding()``
as written in the previous section.
Where using locale encoding as the default encoding is reasonable,
``encoding=io.LOCALE_ENCODING`` will be used instead. For example,
``subprocess`` module will use locale encoding for the default
encoding of the pipes.
Many tests use ``open()`` without ``encoding`` specified to read
ASCII text files. They should be rewritten with ``encoding="ascii"``.
Rationale
@ -174,11 +184,12 @@ Rationale
Opt-in warning
---------------
Although ``DeprecationWarning`` is supressed by default, emitting
``DeprecationWarning`` alwasy when ``encoding`` option is omitted
Although ``DeprecationWarning`` is suppressed by default, emitting
``DeprecationWarning`` always when ``encoding`` option is omitted
would be too noisy.
Noisy warnings may leads developers to dismiss the ``DeprecationWarning``.
Noisy warnings may lead developers to dismiss the
``DeprecationWarning``.
"locale" is not a codec alias