python basic programme exercise

Question

I'm doing a course in udacity, and i got stuck in one exercise. I've changed my code a thousand times but I think that I'm not even close to the righ answer. The exercise is this: define a procedure that takes in a string of numbers from 1-9 and outputs a list with the following parameters: Every number in the string should be inserted into the list. If a number x in the string is less than or equal to the preceding number y, the number x should be inserted into a sublist. Continue adding the following numbers to the sublist until reaching a number z that is greater than the number y. Then add this number z to the normal list and continue. So if the string is '543987' the out put should be [5,[4,3],9,[8,7]].

and my code is:

string = '543987'
def numbers_in_lists(string):
 result = []
 sublist = []
 counter = 0
 ref = 0
 for e in string:
 if e == string[0]:
 result.append(int(e))
 if int(e) < ref:
 sublist.append(int(e))
 else:
 result.append(sublist)
 sublist = []
 result.append(int(e))
 counter = counter + string.find(e)
 ref = int(string[counter])
 return result
print numbers_in_lists(string)
# [5, [], 5, [4, 3], 9] which is not what i expected ([5,[4,3],9,[8,7]])

Is it too bad?? hope someone can help me. Thanks!!

• ChristianFigueroa: 575 fails. It returns [5,7,5] instead of [5,7,[5]] because the first check only checks if the character is equal to the first character, not if it's at the first character's position.
• Joran Beasley: why the down votes? he clearly put some effort in, he posted the problem statement, and the code he tried(which seems like a reasonable attempt to me)
• khelwood: @JoranBeasley But he didn't say what the problem is with the code he posted. So what is he asking?
• Joran Beasley: in his second sentence he posted he was not getting the expected output... ive edited his question to include what his code generates
• Pedro Lopez: @JoranBeasley thank you very much for the help and the corrections!! and i couldn't care less about that guy's downvote, so never mind

Answer 1

there are only two options for each letter in the string

if int(letter) > last_letter:
 if sublist: # if we have any entries in our sublist 
 result.append(sublist) # append them before appending this letter
 sublist = [] # clear sublist
 result.append(int(letter)) # append our letter
else: # it must be lessthan or equal
 sublist.append(int(letter)) # so append to sublist
last_letter = int(letter) # update last_letter

then at the end before you return your result you want to do the same check

if sublist: result.append(sublist)
return result

Answer 2

def numbers_in_lists(string):
 # YOUR CODE
 A = [] #create main list
 B = [] #create sublist
 length = len(string)
 i = 0
 biggest = 0 #initiate biggest number to compare with other number in the string
 while i < length:
 if int(string[i]) > biggest:
 biggest = int(string[i])
 A.append(biggest)
 B = [] #empty sublist to prepare for next round
 else: 
 if B not in A: #prevent adding another sublist B to A
 A.append(B)
 B.append(int(string[i]))
 i += 1 
 return A