Python Patterns: An Optimization Anecdote

Re:Python Patterns: An Optimization Anecdote by njharman on Sunday December 18, 2011 @11:43AM (#3366908)

It's troubling to read something about Python optimization/performance without mention that this is atrocious in a loop

string = string + s

That is such a code smell I cringed every time I saw it.

Should append to list and join at the end (once). Which, I bet (I, or you, don't know anything until we actually profile), dumping the += is significant reason why last two examples where much faster.

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Re:Python Patterns: An Optimization Anecdote by chubot on Sunday December 18, 2011 @01:38PM (#3367157)

I still follow that rule, perhaps somewhat anachronistically. This has been long optimized in CPython so it's not quadratic:

$ python -V

Python 2.5.2

$ python -m timeit -s 'v=["a"]' 'v.append("a")'

1000000 loops, best of 3: 0.199 usec per loop

$ python -m timeit -s 's="a"' 's+="a"'

10000000 loops, best of 3: 0.127 usec per loop

The string append is actually FASTER now. Tried with strings of length 5 and it is still faster.

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