Antoine Pitrou, 25.08.2011 18:58:
Le jeudi 25 août 2011 à 18:50 +0200, Masklinn a écrit :
On 2011-08-25, at 18:40 , Antoine Pitrou wrote:
The most popular (as from what I can see) thing right now where people start seeing that += is slow is when they try to do that on PyPy (which doesn't have hack like CPython, who is still slow) and ask "why my pypy code is sooooo slow".
Different implementations having different performance characteristics is not totally unexpected, is it? (and I'm sure the PyPy developers wouldn't mind adding another hack) This one can not be done, as it relies on knowing there's only one reference to the string (so it can be realloc'd in place), therefore on using a refcounting GC.
Ah, you're right. However, PyPy has another (and quite broader) set of optimizations available: http://codespeak.net/pypy/dist/pypy/doc/interpreter-optimizations.html#strin...
And its JIT could potentially just enable its string-join optimisation automatically when it sees that a variable holds a string, and is never being assigned to inside of a loop or sequence of operations except for the += operator. Any other operation on the string would then just turn it back into a normal string by joining it first. But this is seriously getting off-topic now. Stefan