Given n, generate that many lines of Pascal's Triangle.

pascals_triangle.py

#!/usr/bin/env python3

import sys


def PascalsTriangle(row):
    max_row = int(row)
    triangle = []
    current_row = 0

    while current_row < max_row:
        # These first two cases are short circuits that allow us to ignore
        # the invisible 0s that pad the 1s and can't ignore in these 2 rows
        if current_row == 0:
            members = [1]
        elif current_row == 1:
            members = [1, 1]
        # proceed as normal now that we are passed the first 2 rows
        else:
            pr_index = current_row - 1  # previous row's index
            members = [1]
            members += [triangle[pr_index][x] + triangle[pr_index][x+1]
                        for x in range(pr_index)]
            members += [1]
        triangle.append(members)
        current_row += 1

    return triangle


if __name__ == "__main__":
    try:
        count = sys.argv[1]
        tri = PascalsTriangle(count)
    except Exception as err:
        sys.stderr.write(("\nUsage: pt.py <int>\n"
                          "Example: pt.py 3\n"
                          "\t[[1]\n"
                          "\t[1, 1]\n"
                          "\t[1, 2, 1]]\n"))

    print("\n".join([str(row) for row in tri]))  # print it pretty, print it niiiice