Splitting user input into lists of increasing size [python]

Question

I am trying to produce a code that verifies whether or not a user input meets the criteria of a pascal triangle. I know how to go about inputting the number of lines and having it develop a pascal triangle, but I am having trouble figuring out how to get a user to input something like 1 1 1 1 2 1 1 3 3 1 1 4 6 4 1 1 5 10 10 5 1, and having my program say whether it is a pascal triangle or not.

values = input("Enter the numbers: ").split()

pascals_triangle = list(map(list, values))

I know the first line could split the numbers, and the second line would assign the numbers into individual lists of a list. Every time I attempt to have the lists increase by 1 in every row, I get str/int errors. Once I get past this little road block, I should be able to figure out the rest of the code.

data = input("Enter values: ").split()


def pascal_triangle(data):
    size = int(data[0])
    n = 2 * size + 1
    grid = [[0 for x in range(n)] for y in range(size)]

    left = 1
    for i in range(size, 0, -1):
        grids = data[i].split(' ')
        count = 0
        for g in grids:
            grid[i - 1][left + 2 * count] = int(g)
            count += 1
        left += 1
        if count != i:
            return False

    left = 1
    for i in range(size - 1, -1, -1):
        if i == 0:
            return grid[i][left] == 1
        numbers = i + 1
        count = 0
        while count < numbers:
            current = grid[i][left + count * 2]
            upper_left = grid[i - 1][left - 1 + count * 2]
            upper_right = grid[i - 1][left + 1 + count * 2]
            if current != (upper_left + upper_right):
                return False
            count += 1

        left += 1
    return False



status = pascal_triangle(data)
if status:
    print('It is a pascal triangle')
else:
    print('It is not a pascal triangle')

So, in this code, why am I still not getting the accurate answers?

Show us an attempt where you get it wrong so we can either explain the error or how you go wrong about it. A simple, but generic answer would be to use slices with increasing length. — Reti43, May 24 '18 at 16:58
"Every time I attempt to have the lists....." Can you show your attempt? That would be easier for us too. — Austin, May 24 '18 at 16:58

score 0 · Answer 1 · answered May 24 '18 at 17:10

If you're trying to do this in some fancy way, like adapting the grouper recipe in the itertools docs to take an iterable of group sizes instead of a fixed group size… take a step back and write the "dumb" version first.—just write a loop.

First, split the whole string, the same way you split each line in your line-by-line version.

One thing: mapping list over your values won't do any good; that'll just turn, e.g., '23' into ['2', '3'], and there's not much good you can do with that. You want a list of numbers, which you're then going to break up into a rows (each row also being a list of numbers—the same row you got by mapping int over line.split() in your line-by-line version).

So, here's some pseudocode:

values = input("Enter the numbers: ").split()
nums = [int(value) for value in values]
size = 1
start = 0
while start < len(nums):
    rownums = nums[start:start+size]
    make sure len(rownums) == size
    check rownums the same way you checked each line
    update size and start
if you got here without seeing any errors, it's valid

score 0 · Answer 2 · answered May 24 '18 at 17:30

One way to do this is to generate each row of Pascal's triangle, and use islice to grab a list of the current row length from the user data and see if the data matches the row.

from itertools import islice

def pascal():
    """ Pascal's triangle generator """
    a = [1]
    while True:
        yield a
        #Generate next row from current row
        a = [x + y for x, y in zip([0] + a, a + [0])]

def test_pascal(values):
    it = map(int, values.split())
    ok = True
    for row in pascal():
        data = list(islice(it, len(row)))
        if not data:
            break
        if data != row:
            ok = False
            print('bad data', data, row)
            break
    return ok

# Test

values = '1 1 1 1 2 1 1 3 3 1 1 4 6 4 1 1 5 10 10 5 1'
print(test_pascal(values))

values = '1 1 1 1 2 1 1 3 3 1 1 4 6 5 1'
print(test_pascal(values))

output

True
bad data [1, 4, 6, 5, 1] [1, 4, 6, 4, 1]
False

@random_student `itertools` has some very handy things in it (in fact, it's one of the [built-in modules](https://stackoverflow.com/q/8370206/4014959)), but it does take a little while to learn how to use them effectively. `islice` is pretty simple: `islice(it, n)` says grab the next `n` items from the iterable named `it`. It returns an iterator, so we need to turn that into list. — PM 2Ring, May 25 '18 at 10:17

Splitting user input into lists of increasing size [python]

2 Answers2