On Friday, March 29, 2013 9:58:27 AM UTC+10:30, Dave Angel wrote: > On 03/28/2013 06:11 PM, Eric Parry wrote: > > > On Thursday, March 28, 2013 3:06:02 PM UTC+10:30, Dave Angel wrote: > > > > > > <SNIP> > > >> > > >> > > >> Are you familiar with recursion? Notice the last line in the function > > >> r() calls the function r() inside a for loop. > > >> > > >> So when r() returns, you're back inside the next level up of the > > >> function, and doing a "backtrack." > > >> > > >> When the function succeeds, it will be many levels of recursion deep. > > >> For example, if the original pattern had 30 nonzero items in it, or 51 > > >> zeroes, you'll be 51 levels of recursion when you discover a solution. > > >> > > >> If you don't already understand recursion at all, then say so, and one > > >> or more of us will try to explain it in more depth. > > >> > > <SNIP> > > > > > > Thank you for that explanation. > > > No, I do not understand recursion. It is missing from my Python manual. I > > would be pleased to receive further explanation from anyone. > > > Eric. > > > > > > > Recursion is not limited to Python. It's a general programming term, > > and indeed applies in other situations as well. Suppose you wanted to > > explain what the -r switch meant in the cp command. "r" stands for > > recursion. > > > > (example is from Linux. But if you're more familiar with Windows, it's > > the /s switch in the DIR command.) > > > > The cp command copies all the matching files in one directory to another > > one. If the -r switch is specified, it then does the same thing to each > > subdirectory. > > > > Notice we did NOT have to specify sub-subdirectories, since they're > > recursively implied by the first description. > > > > > > Closer to the current problem, suppose you defined factorial in the > > following way: factorial(0) is 1, by definition. And for all n>0, > > factorial(n) is n*factorial(n-1). > > > > So to directly translate this definition to code, you write a function > > factorial() which takes an integer and returns an integer. If the > > parameter is zero, return one. If the parameter is bigger than zero, > > then the function calls itself with a smaller integer, building up the > > answer as needed (untested). > > > > def factorial(n): > > if n==0: > > return 1 > > val = n *factorial(n-1) > > return val > > > > > > > > > > -- > > DaveA
Thank you for that Dave, I've started writing the VBA code. Eric. -- http://mail.python.org/mailman/listinfo/python-list
