It is kind of you to take the trouble of trying to explain. I see the value assigned to rest on each iteration from the debugging script that I made, What I do not see is how?
Clearly, a = 3, it is constant throughout each iteration, and if rest is equal to 3, then a + rest must be equal to 6. You spoke of drilling down, and I see that mult(3, 2) drills down until b == 0, I am less clear how it then begins to ascend, and if it does, why? But, my question is how is rest assigned a single argument/value? I agree, rest equals 0 (zero) on the first iteration and 3 on the second, but as I don't see how, I cannot understand how value = a + rest => 3+0 => 3 although I get: value = a + rest, and I get (where rest = 0) a + rest => 3+0 and I get 3+0 => 3 What am I missing? Is it something that isn't explicit? It seems to me that rest has two arguments, not one. I do not understand "+>", is it a typo perhaps? Many thanks. -A -----Original Message----- From: Alan Gauld <alan.ga...@btinternet.com> To: tutor@python.org Sent: Wed, 11 Dec 2013 9:05 Subject: Re: [Tutor] recursive function example On 10/12/13 14:48, uga...@talktalk.net wrote: OK, I'll try again, this time just walking through the code from the top. > def mult(a, b): > if b == 0: > return 0 > rest = mult(a, b - 1) > value = a + rest > return value > > print "3 * 2 = ", mult(3, 2) We print "3 * 2 = " and then call mult(3,2) b does not equal zero so we move to the line rest = mult(a,b-1) This calls mult(3,1) Now in the new invocation of mult() b does not equal zero so we move to the line rest = mult(a,b-1) This calls mult(3,0) Now in the new invocation of mult() b does equal zero so we return zero Now back in the mult(3,1) version of mult() rest now equals zero value = a + rest => 3+0 => 3 we return 3 Now back in the original invocation of mult() rest = 3 value = a+rest +> 3+3 => 6 we return 6 we print 6. End of program Remember that each time mult() is called it creates its own mini-world of variables independent of the previous calls. HTH -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ http://www.flickr.com/photos/alangauldphotos _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
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