Printing an ASCII diamond with set width in python

Question

Yes, this is a homework task. But just please, if you\'re going to give me the code please tell me what you\'ve done in detail. I am extremely new to this.

So the ta

Answer 1

One method

The simplest way would probably be have two loops; one counting i up to width, another counting i back down to 1.

width = int(input("Width: "))

i = 1
while i < width:
    print " " * (width-i) + "* " * i
    i += 1

while i > 0:    
    print " " * (width-i) + "* " * i
    i -= 1

This is a bit unattractive because it's a little clumsy, but it's simple.

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Another method

Another method is to have have a loop that counts to twice the width, doing one of two things. What it does depends on if i has passed the point of maximum width or not. So it does 'up' and 'down' in the same loop, counting i from 1 up to width*2.

width = int(input("Width: "))

i = 1
while i < width*2:
    if i < width:
        print " " * (width-i) + "* " * i
    else:
        print " " * (i-width) + "* " * (2*width-i)

    i += 1

This:

 print " " * (width-i) + "* " * i

...is your code. Spaces count from width down to 0, *'s from 1 up to width.

And this:

 print " " * (i-width) + "* " * (2*width-i)

...is the same thing but inverted. Spaces count from 0 back up to width, and the *'s go back down from width to 1. This comes into play when i exceeds width.

Width: 4
   *      # first half does this onward
  * * 
 * * * 
* * * * 
 * * *    # second half does the rest downward
  * * 
   * 

---

And another

Another alternative, more complex way is to use a for loop on a list that contains numbers counting up and down. For example: [1, 2, 3, 2, 1]

To make this list, this code has to be. I know, it's a bit ugly:

rows = []
for i in range(1, max+1):
    rows.append(i)
rows += rows[-2::-1]

Then, you see, we run the for loop off it.

width = int(input("Width: "))

rows = []
for i in range(1, width+1):
    rows.append(i)
rows += rows[-2::-1]    # takes a reversed list and adds it on to the end: [1, 2, 3, 2, 1]

for i in rows:
    print " " * (width-i) + "* " * i

i iterates through each of the numbers in the rows list, which looks something like [1, 2, 3, 2, 1]. Then we just need one printing gizmo.

In python, there's almost always a shorter and less comprehensible way of doing for loops, and in this case, we can get rid of two extra lines by shortening the first for loop:

width = int(input("Width: "))

rows = [ i for i in range(1, width+1)]  # Brain-bending way of doing a for loop 
rows += rows[-2::-1]

for i in rows:
    print " " * (width-i) + "* " * i

And if you're feeling a bit crazy, here's a mere two line version of the whole thing!

width = int(input("Width: "))
print "\n".join([ " "*(width-i) + "* "*i for i in [ i for i in range(1, width+1) ]+[ i for i in range(1, width+1) ][-2::-1] ])

But I don't recommend this style of coding in general.

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Sorry, I got a bit carried away at the end... but the best thing I can say to you now is try everything and play around!

Hope that helps. :)