Question

Ok im back! im on ps3 and have completed part a ( http://dpaste.com/546011/ ) however,Im stuck on part b. I know this is incorrect but here's what i came up with: http://dpaste.com/546014/ help please....

Answer 1

double-oh. i used a list instead of a tuple. this may be cheating but from my understanding, you can't add into a tuple -- they are immutable. so, any command within your loop asking the program to add an index value into a tuple doesn't work. or so i understand. if someone out there knows i am wrong about this, please correct me. here is a copy of my program for that part of problem set 3 if this helps you to see how idid this: http://dpaste.com/546072/

Answer 2

thanks, but the problem clearly states to return a tuple so I need a tuple

Answer 3

found out how to fix your problem. create the list then mutate it into a tuple and return the tuple value. thanks for the help

Answer 4

alicebaker77: you don't have a 'return' statement in your script, and so your function will return 'None', I suppose...

Answer 5

double_o_seven & alicebaker77: I suppose there is no other way but to convert a list to a tuple before the function returns...

Answer 6

I tried to implement recursion in solution ps3b.py as well: http://pastebin.com/MT80xS3h; however, I couldn't find how not to pass 'positions' and 'index' as parameters. In other words, in oder to implement recursion in ps3b.py I passed a list of positions of the key and starting search index as parameters of the function. Strange things happened when I tested my recursive functional implementation.

I can assign default valued to parameters 'positions' and 'index':

def subStringMatchExactRecursive(target, key, positions=[], index=0):

Now, I can supposedly call the function without explicitly passing arguments for parameters 'positions' and 'index':

subStringMatchExactRecursive(target, key)

But if I do this twice in a row:

subStringMatchExactRecursive(target, key)
subStringMatchExactRecursive(target, key)

I will have the correct result first time, but second time the correct result will be appended to the first correct result. If I call the recursive function three times, I will have the correct result the first time, second time I will have two appended correct results in a tuple and third time I will have three correct appended results in a tuple. This seems to be the way Python works. Can somebody explain to me what is really happening during function execution?

Answer 7

double_o_seven & alicebaker77: I found the way to "append" a tuple :-)
a = (1,2)
b = (3,4)
c = a + b
Now c = (1,2,3,4)

Answer 8

For ps3a and ps3b if key == "" what do you think the function should return: an empty string or an index of the target, i.e. a tuple like this: (0,1,2,3,4,...,n) where n is len(target)-1???