python 输出三角形

pattern = input("请输入你要选择的模式：")
while True:
    if pattern == "A":
        row = eval(input("请输入行数："))
        for i in range(, row + ):
            for j in range(, i+):
                print(j, end=" ")
            print("")

    elif pattern == "B":
        row = eval(input("请输入行数："))
        for i in range(, row + ):
            for j in range(, row - i + ):
                print(j, end=" ")
            print("")

    elif pattern == "C":
        row = eval(input("请输入行数："))
        for i in range(, row + ):
            for j in range(row - i, , -):
                print(" ", end=" ")
            for j in range(i, , -):
                print(j, end=" ")
            print("")

    elif pattern == "D":
        row = eval(input("请输入行数："))
        for i in range(, row + ):
            for j in range(, i):
                print(" ", end=" ")
            for j in range(, row - i +  ):
                print(j, end=" ")
            print("")

    elif pattern == "退出":
        break
    else:
        pattern = input("输入错误,请从新输入")