Pascal's triangle in Python.

The program

Press Run to see what it prints. Change anything you like, then run it again.

rows = [[1]]
for i in range(7):
    last = rows[-1]
    new = [1]
    for j in range(len(last) - 1):
        new.append(last[j] + last[j + 1])
    new.append(1)
    rows.append(new)

for row in rows:
    print(" ".join(str(x) for x in row).center(30))

              1               
             1 1              
            1 2 1             
           1 3 3 1            
          1 4 6 4 1           
        1 5 10 10 5 1         
       1 6 15 20 15 6 1       
     1 7 21 35 35 21 7 1      

How it works

1. Each row starts and ends with 1. The numbers in between are the sum of the two numbers above them.
2. The program builds each row from the last one. rows[-1] is the most recent row.
3. center(30) pads the line with spaces so the triangle looks like a triangle. Look for patterns: the sums of the rows are 1, 2, 4, 8, ... the powers of 2.

Try this

• Print more rows.
• Add up each row and check it is a power of 2.
• Print only the odd numbers and see the pattern.

Stuck on an error? Read how to debug Python.