Question

Part 3: Arrows

Write a python program that prompts the user for a number of columns, and them prints the pattern as seen below. You cannot assume that the user will supply positive numbers - if they misbehave you should re-prompt them until they do give you a positive number. Note that your program only has to run one time, but multiple runnings of the program are shown below:

How many columns? 3
*
 *
  *
 *
*

How many columns? 5
*
 *
  *
   *
    *
   *
  *
 *
*

How many columns? 10
*
 *
  *
   *
    *
     *
      *
       *
        *
         *
        *
       *
      *
     *
    *
   *
  *
 *
*

How many columns? -5
Invalid entry, try again!
How many columns? -2
Invalid entry, try again!
How many columns? 6
*
 *
  *
   *
    *
     *
    *
   *
  *
 *
*

Some hints:

• Use separate while loops to make your program easier to understand. One while loop can be used for data validation (negative numbers), another can be used for one half of the arrow structure, and a third can be used for the second half. Break down your program into smaller chunks!
• To produce the pattern shown it will be helpful to create a few accumulator variables. For example, look at the number of spaces before the star character in each line. Do you see a pattern that can be simulated using a while loop?

Now, upgrade your program so that it handles both left and right arrows. Validate your input in the same way you validate the # of columns. Here are a few sample runnings:

How many columns?

How many columns? 5
Direction? (l)eft or (r)ight: l
    *
   *
  *
 *
*
 *
  *
   *
    *

How many columns? 5
Direction? (l)eft or (r)ight: r
*
 *
  *
   *
    *
   *
  *
 *
*

How many columns? 3
Direction? (l)eft or (r)ight: apple
Invalid entry, try again!
How many columns? 4
Direction? (l)eft or (r)ight: l
   *
  *
 *
*
 *
  *
   *

Answer 1

col = int(input('How many columns:'))
while col <= 0:
    print('Invalid entry, try again!')
    col = int(input('How many columns:'))

d = input('Direction? (l)eft or (r)ight: ').lower()
while d not in 'lr':
    print('Invalid entry, try again!')      
    d = input('Direction? (l)eft or (r)ight: ').lower()

spaces = 0 if d == 'r' else (col - 1)

for i in range(col):
    print(' '*spaces + '*')
    spaces += 1 if d == 'r' else -1

spaces = 1 if d == 'l' else (col - 2)
for i in range(col-1, 0, -1):
    print(' '*spaces + '*')
    spaces += -1 if d == 'r' else 1

Please upvote, as i have given the exact answer as asked in question. Still in case of any concerns in code, let me know in comments. Thanks!