On Jul 30, 2007, at 4:13 PM, Ehsan wrote: > hi > coulde any one show me the usage of "yield" keyword specially in this > example: > > > """Fibonacci sequences using generators > > This program is part of "Dive Into Python", a free Python book for > experienced programmers. Visit http://diveintopython.org/ for the > latest version. > """ > > __author__ = "Mark Pilgrim ([EMAIL PROTECTED])" > __version__ = "$Revision: 1.2 $" > __date__ = "$Date: 2004/05/05 21:57:19 $" > __copyright__ = "Copyright (c) 2004 Mark Pilgrim" > __license__ = "Python" > > def fibonacci(max): > a, b = 0, 1 > while a < max: > yield a > a, b = b, a+b > > for n in fibonacci(1000): > print n,
As in how it works? Sure, when you use the yield statement in a function or method you turn it into a generator method that can then be used for iteration. What happens is that when fibonacci(1000) is called in the for loop statement it executes up to the yield statement where it "yields" the then current value of a to the calling context at which point n in the for loop is bound to that value and the for loop executes one iteration. Upon the beginning of the for loop's next iteration the fibonacci function continues execution from the yield statment until it either reaches another yield statement or ends. In this case, since the yield occured in a loop, it will be the same yield statement at which point it will "yield" the new value of a. It should be obvious now that this whole process will repeat until the condition a < max is not longer true in the fibonacci function at which point the function will return without yielding a value and the main loop (for n in ...) will terminate. Erik Jones Software Developer | Emma® [EMAIL PROTECTED] 800.595.4401 or 615.292.5888 615.292.0777 (fax) Emma helps organizations everywhere communicate & market in style. Visit us online at http://www.myemma.com -- http://mail.python.org/mailman/listinfo/python-list