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

[Antoine Pitrou]

Antoine Pitrou <pitrou at free.fr> added the comment:

Well, with the latest patch I get:

$ ./python -m timeit -s "import io; n=2000; d=[b'a'*n,b'bb'*n,b'ccc'*n]*1000"  "s=io.BytesIO(); w=s.write"  "for x in d: w(x)"  "s.getvalue()"
1000 loops, best of 3: 982 usec per loop

$ ./python -m timeit -s "import io; n=2000; d=[b'a'*n,b'bb'*n,b'ccc'*n]*1000"  "s=io.BytesIO(); w=s.write"  "for x in d: w(x)"  "global y; y = s.getvalue()"
100 loops, best of 3: 4.79 msec per loop

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