Python int/str 检查答案

【问题标题】：Python int/str checkingPython int/str 检查
【发布时间】：2011-07-21 21:12:54
【问题描述】：

我有一个家庭作业，我只完成了最低限度的作业，但是在完成它的过程中，我开始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。我想继续这样做，所以如果用户输入 str 作为高度/宽度或其中一个坐标，它会给出错误，但我无法确切地弄清楚如何去做。这是一个介绍类，所以如果你记住，我们只是进入 while 循环，我们已经学习了 for 循环，if/else/etc。

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()

【问题讨论】：

只是想说我喜欢你主动让你的程序更好。 :)

标签： python loops int string

【解决方案1】：

使用.isdigit() 或.isalnum() 检查，看你喜欢什么

例子

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

例子

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

例子

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

【讨论】：

【解决方案2】：

在这种情况下，您需要使用异常处理。基本上这个想法是接受输入并 try 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，输入将始终作为str 提供给您，因此您不能简单地测试它是否是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')

【讨论】：

如果你不喜欢我的isdigit 方法，这就是你要走的路。我只是喜欢这样做，因为它更短，但它具有更广泛的适用性。
@Justin：您的方式也很有效，只需对现有代码进行最少的更改。我只是倾向于这种方式而不是那种方式。 :)
@Ryan：还有一个提示，我会把它放在一个单独的函数中。为您想要执行的每个输入重复此代码块是没有意义的，它只会使您的代码更加混乱。还可以考虑将执行每个形状的代码也移动到单独的函数中。

【解决方案3】：

我会推荐使用

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。

比如这条线

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

会变成

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 中的工作方式不同。在 Python 3.x 中，它应该总是返回一个字符串，因此没有任何理由检查返回的对象是否是一个字符串。

【讨论】：

【解决方案4】：

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

【讨论】：