Python int/str 检查

Question

我有一项家庭作业，并且我已经完成了最低限度的作业，但是在完成它的过程中，我对如何使我的程序变得更好感兴趣。代码的要点是绘制用户定义的形状，并在用户输入无效输入时提供反馈。我想继续这样做，这样如果用户输入高度/宽度或坐标之一的 str ，它就会给出错误，但我无法确切地弄清楚如何做到这一点。这是一门入门课程，所以如果您记住的话，我们只是讨论 while 循环，并且我们已经讨论了 for 循环、if/else/等等。

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，您需要使用异常处理。基本上，其想法是获取输入并尝试转换为int。如果失败，则会引发 ValueError。否则你将得到转换后的值。请记住，输入始终以 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，您可以执行以下操作来不断询问，直到输入正确的值：

# 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()

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

例如，该行将

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

变为

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

“顺便说一下，我假设您正在使用 Python 3.x，否则您的代码将无法工作，因为 input 在 Python 2.x 中的工作方式不同。在 Python 3.x 中，它应该始终返回一个字符串，因此没有任何理由检查返回的对象是否是一个字符串。

Answer 3

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

Answer 4

使用 .isdigit() 或 .isalnum() 检查，具体取决于您喜欢

1. 示例< /p>

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

2. 示例

   str_num= 'aaaa 7777' # 注意有空格
   str_num.isalnum() # false
   str_num.isdigit() # false
   

3. 示例

   <前><代码>str_num='7777'
   str_num.isalnum() # True
   str_num.isdigit() # True
   示例