Serhiy Storchaka <[email protected]> added the comment:
> Honestly, I don't think there's much point in these optimizations. The first
> one ("The sequence length and separator length are both 0") is probably
> useless.
This optimization changes the behavior.
... def __repr__(self): return 'B(' + super().__repr__() + ')'
...
>>> B()
B(b'')
>>> B().join([])
b''
With the patch we get B(b'').
Regardless of whether optimization (which is negligible in this case), I don't
know whether to consider such side effect desirable or undesirable.
bytes.join need to optimize for the 0- and 1-byte delimiter, but the proposed
patch leads to pessimization:
Unpatched:
$ ./python -m timeit -s 'seq=[bytes([i]*100000) for i in range(256)]'
'b"".join(seq)'
10 loops, best of 3: 43.3 msec per loop
Patched:
$ ./python -m timeit -s 'seq=[bytes([i]*100000) for i in range(256)]' 'b"
".join(seq)'
10 loops, best of 3: 70.3 msec per loop
----------
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<http://bugs.python.org/issue12805>
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