Python int / str检查

Question

我有一个家庭作业，并且我已经完成了最少的作业，但是在进行作业时，我对如何使我的程序变得更好感兴趣。 代码的重点是绘制用户定义的形状，并在输入无效输入时提供反馈。 我想继续做下去，所以如果用户输入一个str作为高度/宽度或坐标之一，它将给出一个错误，但是我无法弄清楚该怎么做。 这是一个入门课程，因此，如果您要牢记，我们只是进入while循环，而对于if / else / etc，我们已经进行了循环。

这是我目前拥有的代码：

def draw_user_shape(pen):
    shape = input("Please enter a shape: ")
    while shape != "square" and shape != "rectangle" and shape != "triangle":
        shape = input("Invalid shape, please enter either square, rectangle, or triangle: ")
    if shape == "square":
        h = input("Please enter a height: ")
        while h != int or int(h) < 1:
            h = input("That is an invalid height, please enter an positive integer: ")
        h = int(h)
        c = input("Please enter a color: ")
        while c != str and str(c) != "red" and str(c) != "green" and str(c) != "blue":
            c = input("That is an invalid color, please enter either red, blue, or green: ")
        c = str(c)
        x = input("Please enter an x-coordinate: ")
        while x != int and int(x) == 1:
            x = input("That is an invalid x-coordinate, please enter an integer: ")
        x = int(x)
        y = input("Please enter a y-coordinate: ")
        while y != int and int(y) == int:
            y = input("That is an invalid y-coordinate, please enter an integer: ")
        y = int(y)
        pen.fillcolor(c)
        pen.up()
        pen.goto(x,y)
        pen.down()
        pen.begin_fill()
        pen.goto(x,y+h)
        pen.goto(x+h,y+h)
        pen.goto(x+h,y)
        pen.goto(x,y)
        pen.end_fill()
        pen.up()
    elif shape == "rectangle":
        h = input("Please enter a height: ")
        while h != int and int(h) < 1:
            h = input("That is an invalid height, please enter an positive integer: ")
        h = int(h)
        w = input("Please enter a width: ")
        while w != int and int(w) < 1:
            w = input("That is an invalid height, please enter an positive integer: ")
        w = int(w)
        c = input("Please enter a color: ")
        while c != str and str(c) != "red" and str(c) != "green" and str(c) != "blue":
            c = input("That is an invalid color, please enter either red, blue, or green: ")
        c = str(c)
        x = input("Please enter an x-coordinate: ")
        while x != int and int(x) == 1:
            x = input("That is an invalid x-coordinate, please enter an integer: ")
        x = int(x)
        y = input("Please enter a y-coordinate: ")
        while y != int and int(y) == int:
            y = input("That is an invalid y-coordinate, please enter an integer: ")
        y = int(y)
        pen.fillcolor(c)
        pen.up()
        pen.goto(x, y) 
        pen.down()
        pen.begin_fill()
        pen.goto(x,y+h)
        pen.goto(x+w,y+h)
        pen.goto(x+w,y)
        pen.goto(x,y)
        pen.end_fill()
        pen.up()
    elif shape == "triangle":
        h = input("Please enter a height: ")
        while h != int and int(h) < 1:
            h = input("That is an invalid height, please enter an positive integer: ")
        h = int(h)
        w = input("Please enter a width: ")
        while w != int and int(w) < 1:
            w = input("That is an invalid height, please enter an positive integer: ")
        w = int(w)
        c = input("Please enter a color: ")
        while c != str and str(c) != "red" and str(c) != "green" and str(c) != "blue":
            c = input("That is an invalid color, please enter either red, blue, or green: ")
        c = str(c)
        x = input("Please enter an x-coordinate: ")
        while x != int and int(x) == 1:
            x = input("That is an invalid x-coordinate, please enter an integer: ")
        x = int(x)
        y = input("Please enter a y-coordinate: ")
        while y != int and int(y) == int:
            y = input("That is an invalid y-coordinate, please enter an integer: ")
        y = int(y)
        pen.fillcolor(c)
        pen.up()
        pen.goto(x,y)
        pen.down()
        pen.begin_fill()
        pen.goto(x+w/2,y+h)
        pen.goto(x+w,y)
        pen.goto(x,y)
        pen.end_fill()
        pen.up()

def main():
    import turtle
    pen = turtle.Turtle()
    draw_user_shape(pen)

main()

Answer 1

在这种情况下，您想使用异常处理。 基本上，这个想法是接受输入并尝试将其转换为int 。 如果失败，则会引发ValueError 。 否则，您将取回转换后的值。 请记住，输入将始终以str形式提供给您，因此您不能简单地测试它是否为int 。 假设您使用的是Python 3，则可以执行以下操作来不断询问，直到输入正确的值为止：

# keep asking for input until we get the right one
while True:
    myInput = input('give me a number: ')
    try:
        myValue = int(myInput)
        # if we reach this point, that means we got our number
        break # this will jump out of the loop
    except ValueError:
        # if we reach this point, that means the input was bad
        print('invalid input')

Answer 2

我建议使用

not h.isdigit()

检查字符串h是否不包含整数。 它不适用于浮点数，因为它真正要检查的是每个数字是否在0-9范围内，以及. 将不会（正确）识别为数字。

例如线

while h != int or int(h) < 1:

会成为

while not h.isdigit() or int(h) < 1:

顺便说一句，我假设您使用的是Python 3.x，否则您的代码将无法工作，因为input在Python 2.x中的工作方式有所不同。 在Python 3.x中，它应始终返回字符串，因此没有任何理由检查返回的对象是否为字符串。

Answer 3

>>> isinstance('a', int)
False
>>> isinstance(2, int)
True

Answer 4

使用.isdigit()或.isalnum() 进行检查 ， .isalnum()您的偏好

1. 例

    str_num= 'aaaa7777' str_num.isalnum() # true str_num.isdigit() # false 

2. 例

    str_num= 'aaaa 7777' # Note that has spaces str_num.isalnum() # false str_num.isdigit() # false 

3. 例

    str_num= '7777' str_num.isalnum() # True str_num.isdigit() # True