Printing Simple Diamond Pattern in Python

Question

I would like to print the following pattern in Python 3.5 (I'm new to coding):

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

But I only know how to print the following using the code below, but not sure how to invert it to make it a complete diamond:

n = 5

print("Pattern 1")

for a1 in range (0,n):
    for a2 in range (a1):
        print("*", end="")
    print()

for a1 in range (n,0,-1):
    for a2 in range (a1):
        print("*", end="")
    print()

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

Any help would be appreciated!

Answer 1

Since the middle and largest row of stars has 9 stars, you should make n equal to 9. You were able to print out half of the diamond, but now you have to try to make a function that prints a specific number of spaces, then a specific number of stars. So try to develop a pattern with the number of spaces and stars in each row,

Row1: 4 spaces, 1 star, 4 spaces
Row2: 3 spaces, 3 stars, 3 spaces
Row3: 2 spaces, 5 stars, 2 spaces
Row4: 1 space, 7 stars, 1 space
Row5: 0 spaces, 9 stars, 0 spaces
Row6: 1 space, 7 stars, 1 space
Row7: 2 spaces, 5 stars, 2 spaces
Row8: 3 spaces, 3 stars, 3 spaces
Row9: 4 spaces, 1 star, 4 spaces

So what can you deduce? From row 1 to (n+1)/2, the number of spaces decreases as the number of stars increase. So from 1 to 5, the # of stars = (row number * 2) - 1, while # of spaces before stars = 5 - row number.

Now from row (n+1)/2 + 1 to row 9, the number of spaces increase while the number of stars decrease. So from 6 to n, the # of stars = ((n+1 - row number) * 2) - 1, while # of spaces before stars = row number - 5.

From this information, you should be able to make a program that looks like this,

n = 9
print("Pattern 1")
for a1 in range(1, (n+1)//2 + 1): #from row 1 to 5
    for a2 in range((n+1)//2 - a1):
        print(" ", end = "")
    for a3 in range((a1*2)-1):
        print("*", end = "")
    print()

for a1 in range((n+1)//2 + 1, n + 1): #from row 6 to 9
    for a2 in range(a1 - (n+1)//2):
        print(" ", end = "")
    for a3 in range((n+1 - a1)*2 - 1):
        print("*", end = "")
    print()

Note that you can replace n with any odd number to create a perfect diamond of that many lines.

Answer 2

Here is a solution base on height equals to top to the middle, or half of the height. For example, height is entered as 4(7) or 5(9) below. This method will yield odd number actual height

h = int(input("please enter diamond's height:"))

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

# please enter diamond's height:4
#      *
#     ***
#    *****
#   *******
#    *****
#     ***
#      *
#
# 3, 2, 1, 0, 1, 2, 3  space
# 1, 3, 5, 7, 5, 3, 1  star

# please enter diamond's height:5
#       *
#      ***
#     *****
#    *******
#   *********
#    *******
#     *****
#      ***
#       *
#
# 4, 3, 2, 1, 0, 1, 2, 3, 4  space
# 1, 3, 5, 7, 9, 7, 5, 3, 1  star

Here is another solution base on height equals to top to the bottom, or the actual total height. For example, height is entered as 7 or 9 below. When the user enters an even number for height, the diamond will be slightly slanted.

h = int(input("please enter diamond's height:"))

for i in range(1, h, 2):
    print(" "*(h//2-i//2), "*"*i)
for i in range(h, 0, -2):
    print(" "*(h//2-i//2), "*"*i)

# please enter diamond's height:7
#      *
#     ***
#    *****
#   *******
#    *****
#     ***
#      *
#
# 3, 2, 1, 0, 1, 2, 3  space
# 1, 3, 5, 7, 5, 3, 1  star
#
# please enter diamond's height:9
#       *
#      ***
#     *****
#    *******
#   *********
#    *******
#     *****
#      ***
#       *
#
# 4, 3, 2, 1, 0, 1, 2, 3, 4  space
# 1, 3, 5, 7, 9, 7, 5, 3, 1  star