Today I challenged myself to try and implement a recursive function that would produce Pascal's Triangle up to n levels. I managed to come up with a solution, however, it is not as efficient or elegant as I would like. In the following code, each time I call pascal_row() in pascal(), it has iterate through whatever number of levels is passed to pascal_row(); opposed to having it go through and build the triangle in n levels. I don't know if that makes sense, but here is the code... is there anyway to optimize this?

#builds the pascal row for the specified level
#ex. pascal_row(3) --> [1,3,3,1]
def pascal_row(levels):
    if levels == 0:
        return [1]
    elif levels == 1:
        return [1,2,1]
    else:
        row = []
        row.append(1)
        prev = pascal_row(levels-1)
        for i in range(len(prev)):
            try:
                row.append(prev[i] + prev[i+1])
            except:
                pass
        row.append(1)
        return row

#prints out pascal triangle up to specified level
def pascal(levels):
    for lvl in range(levels):
        print(pascal_row(lvl))

if __name__ == "__main__":
    pascal(10)  #outputs correctly