[issue15381] Optimize BytesIO to do less reallocations when written, similarly to StringIO

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

Benchmark from issue22003:

$ ./python0 -m timeit -s 'import i' 'i.readlines()'

Before patch: 10 loops, best of 3: 36.1 msec per loop
After patch: 10 loops, best of 3: 27.5 msec per loop

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<http://bugs.python.org/issue15381>
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