Diamond pattern in Python

A diamond is a centred pyramid with an upside-down pyramid under it. The first loop prints the top half, and the second loop prints the bottom half in reverse order.

The program

n = int(input("Rows in the top half: "))

for i in range(1, n + 1):
    print(" " * (n - i) + "*" * (2 * i - 1))

for i in range(n - 1, 0, -1):
    print(" " * (n - i) + "*" * (2 * i - 1))

Typed in this example: 4. Press Run to type your own.

Rows in the top half: 4
   *
  ***
 *****
*******
 *****
  ***
   *

How it works

• Row i has 2 * i - 1 stars (1, 3, 5, 7) and n - i spaces in front.
• range(n - 1, 0, -1) counts down from 3 to 1. It starts at n - 1 so that the widest row is printed only once.
• The spaces go only in front of the stars, so no line ends with a space.

A hollow diamond

For an outline, each row prints a star, then spaces, then a second star. The top and bottom rows have only one star:

n = 4

for i in list(range(1, n + 1)) + list(range(n - 1, 0, -1)):
    width = 2 * i - 1
    if width == 1:
        row = "*"
    else:
        row = "*" + " " * (width - 2) + "*"
    print(" " * (n - i) + row)

   *
  * *
 *   *
*     *
 *   *
  * *
   *

• list(range(1, 5)) + list(range(3, 0, -1)) gives [1, 2, 3, 4, 3, 2, 1], so a single loop prints both halves.
• width - 2 is the number of spaces between the two stars on each row.

For a single pyramid, see the star triangle pattern.