python - Python 中的帕斯卡三角形问题

Question

我面临的唯一问题是断言语句。我需要确保用户仅输入大于零的整数，而不输入任何字符或符号。如果用户输入字符或符号，则断言语句应打印错误语句。我已经尝试过 isinstance(), type(variable) == int 但我只收到名称错误。有没有不用if的方法？

def PascalTriangle(rows):

    ptriangle = [[1], [1, 1]]
    if rows == 1:
        return ptriangle[0]
    else:
        for rownumber in range(2, rows):
            ptriangle.append([1]*rownumber)
            for number in range(1, rownumber):
                ptriangle[rownumber][number] = (ptriangle[rownumber-1][number-1]+ptriangle[rownumber-1][number])                           
                ptriangle[rownumber].append(1)
        return ptriangle

def PrintPascalTriangle(ptriangle):

    largest_element = ptriangle[-1][len(ptriangle[-1]) // 2]
    element_width = len(str(largest_element))
    def format_row(row):
        return ' '.join([str(element).center(element_width) for element in row])
    triangle_width = len(format_row(ptriangle[-1]))
    for row in ptriangle:
        print(format_row(row).center(triangle_width))

rows = input('Enter the number of rows in Pascal`s Triangle: ')
assert (rows > 0),"Number of rows should be greater than zero"
PrintPascalTriangle(PascalTriangle(rows)) 

Answer 1

.isdigit() 检查输入是否可以是正整数。 while not 让用户进入循环，直到输入正整数。

rows = raw_input("Question")
while not rows.isdigit():
    print"That is not a positive int!"
    rows = raw_input("Question")
rows = int(rows)