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(1, row + 1):
            for j in range(1, i+1):
                print(j, end=" ")
            print("")

    elif pattern == "B":
        row = eval(input("请输入行数："))
        for i in range(1, row + 1):
            for j in range(1, row - i + 2):
                print(j, end=" ")
            print("")

    elif pattern == "C":
        row = eval(input("请输入行数："))
        for i in range(1, row + 1):
            for j in range(row - i, 0, -1):
                print(" ", end=" ")
            for j in range(i, 0, -1):
                print(j, end=" ")
            print("")

    elif pattern == "D":
        row = eval(input("请输入行数："))
        for i in range(1, row + 1):
            for j in range(1, i):
                print(" ", end=" ")
            for j in range(1, row - i + 2 ):
                print(j, end=" ")
            print("")

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