Number half Pyramid Python

Question

I'm trying to print a half pyramid that stars on the left side in python. So far, this is my code

for i in range(1,12):
    for j in range(12 - i):
        print(" ", end = " ")
    for j in range(1, i):
        print(j, end = " " )
    print("\n")

and my output is

                    1 

                  1 2 

                1 2 3 

              1 2 3 4 

            1 2 3 4 5 

          1 2 3 4 5 6 

        1 2 3 4 5 6 7 

      1 2 3 4 5 6 7 8 

    1 2 3 4 5 6 7 8 9 

  1 2 3 4 5 6 7 8 9 10

However, my output is meant to be in the opposite order:

How can I make this change?

score 2 · Answer 1 · answered Feb 27 '17 at 22:48

2

Just reverse the second loop -- the one that prints that actual numbers:

for j in range(i-1, 0, -1):

The last parameter controls the "step", or how much the variable changes on each loop iteration. Output:

answered Feb 27 '17 at 22:48

Prune

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so just to confirm the code you entered : the range is i(12) - 1 to 0 and goes down by 1 in each iteration? – fijilemon12 Feb 27 '17 at 22:49
Right. The parameters are start, stop, and step. The loop doesn't include the stop value. – Prune Feb 27 '17 at 22:51
Great. Remember to up-vote helpful things and to accept one of the answers. This allows SO to properly archive the question. – Prune Feb 27 '17 at 23:02

score 2 · Answer 2 · answered Feb 27 '17 at 22:56

Reverse the range by adding the third argument (-1). Also format your numbers to use 2 places, so 10 is not pushing the last line to the right. Finally, the last print should probably not have \n, since that is already the default ending character of print:

for i in range(1,12):
    for j in range(12 - i):
        print("  ", end = "")
    for j in range(i-1, 0,-1):
        print(str(j).rjust(2), end = "" )
    print()

score 1 · Answer 3 · answered Feb 27 '17 at 22:49

1

You could just reverse the range that you print out as numbers

for i in range(1,12):
    for j in range(12 - i):
        print(" ", end = " ")
    for j in reversed(range(1, i)):
        print(j, end = " " )
    print("\n")

answered Feb 27 '17 at 22:49

Paul Rooney

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so when you write ` for j in reversed(range(1, i)):` is reversed a method or ? – fijilemon12 Feb 27 '17 at 22:58
[reversed](https://docs.python.org/3.3/library/functions.html#reversed) is just a built in free function, which returns a copy the input but in reverse. There is also [.reverse](https://docs.python.org/3/library/stdtypes.html#mutable-sequence-types), which is a method and reverses a mutable sequence in place, returning `None`. – Paul Rooney Feb 27 '17 at 23:02

score 0 · Answer 4 · answered Feb 27 '17 at 22:55

The problem is in your second for loop, as you are looping from 1 to i, meaning you start off with 1 being printed first, and every following number until (not including) i.

Fortunately, for loops are able to go in reverse. So, instead of:

for j in range(1, i)

You could write:

for j in range((i-1), 0, -1)

Where the first parameter is signifies where the loop starts, the second is where the loop finishes, and the third signifies how large our jumps are going to be, in this case negative. The reason we are starting at i-1 and finishing at 0 is because loops start at exactly the first given number, and loop until just before the second given number, so in your given code the loop stops just before i, and so this one starts just before i as well, although you could remove the -1 if you wish to include 12 in the pyramid.

Number half Pyramid Python

4 Answers4