On Sun, 05 Feb 2006 03:31:24 +0000, Neil Schemenauer wrote: > Peter Hansen <[EMAIL PROTECTED]> wrote: >> More precisely, the state of the function is *saved* when a yield >> occurs, so you certainly don't *recreate* it from scratch, but merely >> restore the state, and this should definitely be faster than creating it >> from scratch in the first place. > > Right. Resuming a generator is faster than calling a function.
Have you actually measured this, or are you just making a wild guess? According to a short test performed by Magnus Lycka, resuming a generator takes more time than calling a function. My own test agrees. Here is my test, using Python 2.3. I've tried to make the test as fair as possible, with the same number of name lookups in both pieces of test code. # straight function, two name lookups >>> import timeit >>> >>> t1 = timeit.Timer(stmt="func.next()", setup= ... """class K: ... pass ... ... def next(): ... return 1 ... ... func = K() ... func.next = next ... """) >>> >>> t1.timeit() 0.63980388641357422 # generator, two name lookups >>> t2 = timeit.Timer(stmt="gen.next()", setup= ... """def g(): ... while 1: yield 1 ... ... gen = g() ... """) >>> >>> t2.timeit() 0.82081794738769531 # straight function, one name lookup >>> t3 = timeit.Timer(stmt="f()", setup= ... """def f(): ... return 1 ... """) >>> >>> t3.timeit() 0.47273492813110352 # generator, one name lookup >>> t4 = timeit.Timer(stmt="gnext()", setup= ... """def g(): ... while 1: yield 1 ... ... gnext = g().next ... """) >>> >>> t4.timeit() 0.55085492134094238 So on the basis of my tests, there is a small, but significant speed advantage to _calling_ a function versus _resuming_ a generator. Of course the other advantages of generators often far outweigh the tiny setup cost each time you call one. In addition, for any complex function with significant execution time, the call/resume time may be an insignificant fraction of the total execution time. There is little or no point in avoiding generators due to a misplaced and foolish attempt to optimise your code. -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
