nums_in_lists

# defines 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.

def numbers_in_lists(string):
    """
    Takes a string of numbers as input and outputs a list.
    """
    # create empty lists: result list and buffer list
    result = []
    buffer_list = []
    compare = int(string[0])
    
    # check if input is not empty
    if len(string) >= 1:
        # append first element to result list
        result.append(int(string[0]))
        
        idx = 1
        # iterate through rest of the elements of the string
        while idx < len(string):        
            # if the num at the next position is greater
            if int(string[idx]) > compare:
                # see if something in buffer, add to result, empty buffer
                if buffer_list:
                    result.append(buffer_list)
                    buffer_list = []                
                # set that bigger number as the new comparison value
                compare = int(string[idx])
                # append it to result list
                result.append(compare)
            else:
                # if num at next pos is smaller, add to buffer and continue
                buffer_list.append(int(string[idx]))
            idx = idx + 1
        # if still something in buffer, add to result at very end
        if buffer_list:
            result.append(buffer_list)
    return result


#testcases

string = '543987'
result = [5,[4,3],9,[8,7]]
print repr(string), numbers_in_lists(string) == result
string= '987654321'
result = [9,[8,7,6,5,4,3,2,1]]
print repr(string), numbers_in_lists(string) == result
string = '455532123266'
result = [4, 5, [5, 5, 3, 2, 1, 2, 3, 2], 6, [6]]
print repr(string), numbers_in_lists(string) == result
string = '123456789'
result = [1, 2, 3, 4, 5, 6, 7, 8, 9]
print repr(string), numbers_in_lists(string) == result