Fredrik Lundh wrote: > Frank Millman wrote: > > > I have found two ways of doing it that seem to work. > > > > 1 - row = table[23][:] > > > > 2 - row = [] > > row[:] = table[23] > > > > Are these effectively identical, or is there a subtle distinction which > > I should be aware of. > > > > I did some timing tests, and 2 is quite a bit faster if 'row' > > pre-exists and I just measure the second statement. > > quite a bit ? maybe if you're using very short rows, and all rows > have the same length, but hardly in the general case: > > python -mtimeit -s "data=[range(100)]*100; row = []" "row[:] = data[23]" > 100000 loops, best of 3: 5.35 usec per loop > > python -mtimeit -s "data=[range(100)]*100" "row = data[23][:]" > 100000 loops, best of 3: 4.81 usec per loop > > (for constant-length rows, the "row[:]=" form saves one memory > allocation, since the target list can be reused as is. for longer rows, > other things seem to dominate) > > </F>
Interesting. My results are opposite. python -mtimeit -s "data=[range(100)]*100; row = []" "row[:] = data[23]" 100000 loops, best of 3: 2.57 usec per loop python -mtimeit -s "data=[range(100)]*100" "row = data[23][:]" 100000 loops, best of 3: 2.89 usec per loop For good measure, I tried Rune's suggestion - python -mtimeit -s "data=[range(100)]*100" "row = list(data[23])" 100000 loops, best of 3: 3.69 usec per loop For practical purposes these differences are immaterial - I do not anticipate huge quantities of data. If they are all equivalent from a functional point of view, I lean towards the second version. I agree with Rune that the third one is nicer to read, but somehow the [:] syntax makes it a bit more obvious what is going on. Thanks Frank -- http://mail.python.org/mailman/listinfo/python-list
