print yanghui triangle

yanghui_triangle.py

def yanghui_triangle():
    def safe_get_value(l, index):
        length = len(l)
        return 0<= index < length and l[index] or 0
        
    tmp = [1]
    while True:
        yield tmp
        length = len(tmp)
        new = []
        for idx in range(length+1):
            item = safe_get_value(tmp, idx-1) + safe_get_value(tmp, idx)
            new.append(item)
        tmp = new

if __name__ == '__main__':
    yh_gen = yanghui_triangle()
    for _ in range(10):
       print next(yh_gen)