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gh-70546: Document mmap object's __iter__ behavior that differs from that of bytearray. #140284

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gh-70546: Document mmap object's __iter__ behavior that differs from that of bytearray. #140284

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7 changes: 7 additions & 0 deletions Doc/library/mmap.rst
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Expand Up @@ -16,6 +16,13 @@ byte by doing ``obj[index] = 97``, or change a subsequence by assigning to a
slice: ``obj[i1:i2] = b'...'``. You can also read and write data starting at
the current file position, and :meth:`seek` through the file to different positions.

.. note::
Iterating over a mmap object yields :class:`bytes` objects of length 1; this
differs from :class:`bytearray` which yields :class:`int` values in the range
[0, 255]. This behavior has been retained for backwards-compatibility. To get
an iterator that iterates over bytes you can create a :class:`memoryview` object
referencing the mmap object.

A memory-mapped file is created by the :class:`~mmap.mmap` constructor, which is
different on Unix and on Windows. In either case you must provide a file
descriptor for a file opened for update. If you wish to map an existing Python
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