Question

from string import *
def subStringMatch1(target,key):
i=0
c=0
tup=()
while c!=-1:
c = find(target,key,i)
if c!=-1:
tup = tup + (c,) # print c
i=c+1
return tup

def newFunction(target,key):
length=len(key)

for i in range(0,length):
#print i
key1=key[0:i]
key2=key[i+1:length]
starts1=subStringMatch1(target,key1)
starts2=subStringMatch1(target,key2)
## m=len(starts1)
## for s in range(0,m):
## for z in range(0,m):
# print starts1

Answer 1

Your subStringMatch1() is great!
Yet, what if key == ""? Should the function return an empty tuple or the target?

Answer 2

Thanks !
you mean I should apply a some defensive programming, right ?
one more problem I have is that I would need to write the next function with (target) as a tuple. how do I have a function expect a tuple ?

Answer 3

I don't think it's defensive programming. I think it's conceptual. I would even call it a bug because I figured this question out when I started implementing further functions.
Just imagine: if you are searching for 'nothing' why should the function return 'nothing'? I should probably return 'the whole'. This concept was not obvious to me until I started on the later problems of ps3, and so my initial StringMatch function returned an empty tuple when it searched the target for an empty key.

A tuple can be passed to a function as an argument. Did I understand you question correctly? You are confused that you will have to pass a tuple as an argument to a function, right?

Answer 4

hmm, that makes sense.

And yes. The next step in problem 3 was to create a def that would take 2 tuples as as arguments. I'm a little confused here although the answer is probably simple... right .. ?

Answer 5

you can refer to elements of a tuple the same way you would refer to elements of a list, for example, if tuple = (1,2,3,4) then tuple[0] would equal 1, tuple[1] would equal 2 and do forth.

Answer 6

how do you use it a function (where you don't know how long the tuple is?

def constrainedMatchPair(tuple1,tuple2,len) ?
so when I actually try to execute it, would it look like :
constrainedMatchPair(1,2,3,4) ? or constrainedMatchPair((1,2),(3.4),5) ?

Answer 7

I got it ...... easy.
Is it possible that they have an error in their function ? I'm gettıng an error here
def subStringMatchOneSub(target,key):
"""search for all locations of key in target, with one substitution"""
allAnswers = ()
for miss in range(0,len(key)):
# miss picks location for missing element
# key1 and key2 are substrings to match
key1 = key[:miss]
key2 = key[miss+1:]
print 'breaking key',key,'into',key1,key2
# match1 and match2 are tuples of locations of start of matches
# for each substring in target
match1 = subStringMatchExact(target,key1)
match2 = subStringMatchExact(target,key2)
print match1,match2
# when we get here, we have two tuples of start points
# need to filter pairs to decide which are correct
filtered = constrainedMatchPair(match1,match2,len(key1))
allAnswers = allAnswers + filtered
print 'match1',match1
print 'match2',match2
print 'possible matches for',key1,key2,'start at',filtered
return allAnswers

Answer 8

nevermind I've got it :P

Answer 9

I think in order to stop errors you have to make sure your subStringMatchExact() and constrainedMatchPair() work without errors.