Peter Otten wrote: > Steve Holden wrote: > >> Phoe6 wrote: >>> On May 19, 2:23 pm, Raymond Hettinger <[EMAIL PROTECTED]> wrote: >>>> Instead of: >>>> short_path = mdists[0] >>>> if mdists.count(short_path) > 1: >>>> write: >>>> short_path = mdists[0] >>>> if short_path in mdists[1:]: >>> I would like to understand the difference between the two if >>> statements. >>> I had used count method, to signify the meaning that, if the least >>> distance occurs more then proceed with block. >>> How is 'in' with list[1:] an advantage? If it is. >> Because it can stop as soon as short_path is found, whereas the count >> method must examine all elements to determine whether they should >> increment the count beyond one. > > It's a trade-off. You check only half (on average) of the items in the > original list, but in exchange copy all but one into a new list. > The idiom Raymond recommended only makes sense because comparison is "slow" > and slicing is "fast" in Python. > That's true.
> If the original list were large in comparison to the available RAM the > following idiom might be preferrable: > > it = iter(mdists) > short_path = it.next() > if short_path in it: > # ... Yes, that would nail it. Though of course it loses the obviousness which both original solutions have. I suppose that's often the nature of optimizations, though. regards Steve -- Steve Holden +1 571 484 6266 +1 800 494 3119 Holden Web LLC/Ltd http://www.holdenweb.com Skype: holdenweb http://del.icio.us/steve.holden ------------------ Asciimercial --------------------- Get on the web: Blog, lens and tag your way to fame!! holdenweb.blogspot.com squidoo.com/pythonology tagged items: del.icio.us/steve.holden/python All these services currently offer free registration! -------------- Thank You for Reading ---------------- -- http://mail.python.org/mailman/listinfo/python-list
