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bpo-39357: Remove buffering parameter of bz2.BZ2File (GH-18028)
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Remove the buffering parameter of bz2.BZ2File. Since Python 3.0, it
was ignored and using it was emitting a DeprecationWarning. Pass an
open file object to control how the file is opened.

The compresslevel parameter becomes keyword-only.
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vstinner authored Jan 16, 2020
1 parent c5b7900 commit 9baf242
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Showing 5 changed files with 26 additions and 15 deletions.
14 changes: 8 additions & 6 deletions Doc/library/bz2.rst
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Expand Up @@ -65,7 +65,7 @@ All of the classes in this module may safely be accessed from multiple threads.
Accepts a :term:`path-like object`.


.. class:: BZ2File(filename, mode='r', buffering=None, compresslevel=9)
.. class:: BZ2File(filename, mode='r', *, compresslevel=9)

Open a bzip2-compressed file in binary mode.

Expand All @@ -81,8 +81,6 @@ All of the classes in this module may safely be accessed from multiple threads.
If *filename* is a file object (rather than an actual file name), a mode of
``'w'`` does not truncate the file, and is instead equivalent to ``'a'``.

The *buffering* argument is ignored. Its use is deprecated since Python 3.0.

If *mode* is ``'w'`` or ``'a'``, *compresslevel* can be an integer between
``1`` and ``9`` specifying the level of compression: ``1`` produces the
least compression, and ``9`` (default) produces the most compression.
Expand Down Expand Up @@ -110,9 +108,6 @@ All of the classes in this module may safely be accessed from multiple threads.
.. versionadded:: 3.3


.. deprecated:: 3.0
The keyword argument *buffering* was deprecated and is now ignored.

.. versionchanged:: 3.1
Support for the :keyword:`with` statement was added.

Expand All @@ -138,6 +133,13 @@ All of the classes in this module may safely be accessed from multiple threads.
.. versionchanged:: 3.6
Accepts a :term:`path-like object`.

.. versionchanged:: 3.9
The *buffering* parameter has been removed. It was ignored and deprecated
since Python 3.0. Pass an open file object to control how the file is
opened.

The *compresslevel* parameter became keyword-only.


Incremental (de)compression
---------------------------
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10 changes: 10 additions & 0 deletions Doc/whatsnew/3.9.rst
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Expand Up @@ -420,6 +420,12 @@ Removed
3.5 (:issue:`22486`): use :func:`math.gcd` instead.
(Contributed by Victor Stinner in :issue:`39350`.)

* The *buffering* parameter of :class:`bz2.BZ2File` has been removed. Since
Python 3.0, it was ignored and using it was emitting
:exc:`DeprecationWarning`. Pass an open file object to control how the file
is opened.
(Contributed by Victor Stinner in :issue:`39357`.)


Porting to Python 3.9
=====================
Expand Down Expand Up @@ -451,6 +457,10 @@ Changes in the Python API
:data:`~errno.EBADF` error.
(Contributed by Victor Stinner in :issue:`39239`.)

* The *compresslevel* parameter of :class:`bz2.BZ2File` became keyword-only,
since the *buffering* parameter has been removed.
(Contributed by Victor Stinner in :issue:`39357`.)


CPython bytecode changes
------------------------
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10 changes: 1 addition & 9 deletions Lib/bz2.py
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Expand Up @@ -24,8 +24,6 @@
# Value 2 no longer used
_MODE_WRITE = 3

_sentinel = object()


class BZ2File(_compression.BaseStream):

Expand All @@ -38,7 +36,7 @@ class BZ2File(_compression.BaseStream):
returned as bytes, and data to be written should be given as bytes.
"""

def __init__(self, filename, mode="r", buffering=_sentinel, compresslevel=9):
def __init__(self, filename, mode="r", *, compresslevel=9):
"""Open a bzip2-compressed file.
If filename is a str, bytes, or PathLike object, it gives the
Expand All @@ -65,12 +63,6 @@ def __init__(self, filename, mode="r", buffering=_sentinel, compresslevel=9):
self._closefp = False
self._mode = _MODE_CLOSED

if buffering is not _sentinel:
warnings.warn("Use of 'buffering' argument is deprecated and ignored "
"since Python 3.0.",
DeprecationWarning,
stacklevel=2)

if not (1 <= compresslevel <= 9):
raise ValueError("compresslevel must be between 1 and 9")

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3 changes: 3 additions & 0 deletions Lib/test/test_bz2.py
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Expand Up @@ -100,6 +100,9 @@ def testBadArgs(self):
self.assertRaises(ValueError, BZ2File, os.devnull, compresslevel=0)
self.assertRaises(ValueError, BZ2File, os.devnull, compresslevel=10)

# compresslevel is keyword-only
self.assertRaises(TypeError, BZ2File, os.devnull, "r", 3)

def testRead(self):
self.createTempFile()
with BZ2File(self.filename) as bz2f:
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Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
Remove the *buffering* parameter of :class:`bz2.BZ2File`. Since Python 3.0, it
was ignored and using it was emitting :exc:`DeprecationWarning`. Pass an open
file object, to control how the file is opened. The *compresslevel* parameter
becomes keyword-only.

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