Hi Wesley,
Thank you very much for the feeback. It helped a lot! Quoting wesley chun <[EMAIL PROTECTED]>: >> def lines(file): >> for line in file: yield line >> yield '\n' >> >> del blocks(file): >> block = [] >> for line in lines(file): >> if line.strip(): >> block.append(line) >> elif block: >> yield ''.join(block).strip() >> block = [] >> >> 1.) Does the yield mean the block list is returned from the function >> AND then wiped out by 'block = []'? > > the code in question will take all the strings in block, concatenate > them together [with ''.join()], remove leading/trailing whitespace > [.strip()], and yield or "return" it as the next "generated" item > being iterated over. when .next() is executed again, either > explicitly by the caller or via a for-loop, it will resume immediately > on the next line succeeding the yield statement where execution was > paused. > > >> 2.) Is block list scrubbed clean by 'block = []' because the function >> is going to iterate over the next block and it needs to be empty? > > yes, block is then cleared so that it can process the next few lines of data. > > >> 3.) The statement after the 'yield' threw me. I haven't seen that to >> this point in the book. I figured 'yield' is always last in a function >> because it needs to iterate over itself again. Am I understanding >> generators correctly? > > a "yield" does *not* have to be the last in the function. wherever a > yield is encountered, the function will resume right after it when > .next() is called again. generators do "not start from scratch...," > they pick up right where they left off. > > >> 4.) Is it correct to say that a generator is a function that returns >> multiple values and iterates over itself? > > a generator acts like an iterator in that multiple values are returned > in an iterative process (meaning not all at the same time). it is > dressed up as a function which contains logic that can "generate" each > successive value to "return." > > i have to give kudos to magnus for putting "real world" code when he > teaches generators in his book. for my core python book, i was more > concerned about getting the point across as to what generators *are*, > so for completeness, here are some of the examples i used, all of > which can be downloaded at the book's website (see below) regardless > of whether you buy the book (or not): > > 1) simpleGen.py (the world's 2nd simplest generator?): > > def simpleGen(): > yield 1 > yield '2 --> punch!' > > if __name__ == '__main__': > for item in simpleGen(): > print item > > 2) randGen.py: > > from random import randrange as rr > > def randGen(aList): > while aList: > yield aList.pop(rr(len(aList))) > > if __name__ == '__main__': > for item in randGen(['rock', 'paper', 'scissors']): > print item > > 3) counter.py (needs 2.5+): > > def counter(start_at=0): > count = start_at > while True: > val = (yield count) > if val is not None: > count = val > else: > count += 1 > > if __name__ == '__main__': > print 'initializing counter to start counting at 5' > count = counter(5) > print 'calling count.next():', count.next() > print 'calling count.next():', count.next() > print 'calling count.send(9):', count.send(9) > print 'calling count.next():', count.next() > print 'calling count.close():', count.close() > print 'calling count.next():', count.next() > > you can get these by clicking on "Source Code" -> ch11 -> alt. i'll > leave it as an exercise to reader to determine the output *and WHY*. > :-) another fun place to go look for iterators is the itertools > module. it contains a lot of useful iteration code that are all > really just generators(!): > > http://docs.python.org/lib/itertools-functions.html > > hope this helps! > -- wesley > - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - > "Core Python Programming", Prentice Hall, (c)2007,2001 > http://corepython.com > > wesley.j.chun :: wescpy-at-gmail.com > python training and technical consulting > cyberweb.consulting : silicon valley, ca > http://cyberwebconsulting.com Regards, Josh. _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
