Draw an M-shaped pattern with nested loops

Question

I just started Python 2.7 very recently, but I\'m stuck at this a problem:

Make a program that prints an \"M\" pattern of asterisks. The user shall in

Answer 1

Sometimes it helps to sketch out a table of the values you need to generate:

h notch_rows  no_notch_rows  row   "*"s  " "s  "*"s

3     1                       1     1     1     1
                     2        1     3
                              2     3

5     2                       1     1     3     1
                              2     2     1     2
                     3        1     5
                              2     5
                              3     5

7     3                       1     1     5     1
                              2     2     3     2
                              3     3     1     3
                     4        1     7
                              2     7
                              3     7
                              4     7

---

This results in an implementation like

def mstar(h, star_ch="*", space_ch=" "):
    assert h % 2, "h must be odd"

    notch_rows    = h // 2
    no_notch_rows = notch_rows + 1
    rows          = []

    for row in range(1, notch_rows + 1):
        stars  = star_ch  * row
        spaces = space_ch * (h - 2 * row)
        rows.append(stars + spaces + stars)

    for row in range(1, no_notch_rows + 1):
        stars  = star_ch * h
        rows.append(stars)

    return "\n".join(rows)

def main():
    h = int(input("Height of M-Star? "))    # use raw_input for Python 2.x
    print(mstar(h))

if __name__ == "__main__":
    main()

and runs like

Height of M-Star? 5
*   *
** **
*****
*****
*****

Height of M-Star? 9
*       *
**     **
***   ***
**** ****
*********
*********
*********
*********
*********