Question

我的目标：允许用户仅输入0或1（总共4个变量）。如果用户输入例如2,1,1,0，则应该抛出错误Only 0 and 1 allowed。

到目前为止我尝试过的事情：

if (firstBinary != 0 or firstBinary != 1 and secondBinary != 0
      or secondBinary != 1 and thirdBinary != 0 or thirdBinary != 1
      and forthBinary != 0 or forthBinary != 1):
    print('Only 0 and 1 allowed')
else:
    print('binary to base 10: result)

问题：当我使用这样的陈述时，即使我输入例如5，我也得到结果，或者我得到的只有0和1允许＆＃39;即使我写了全部1或0。

我发现这似乎是我追求的，但它仍然没有像我想要的那样工作：

if 0 in {firstBinary, secondBinary, thirdBinary, forthBinary} or 1 in \
    {firstBinary, secondBinary, thirdBinary, forthBinary}:
    print("Your result for binary to Base 10: ", allBinaries)
else:
    print('Only 0 and 1 allowed')

这段代码基本上给了我与第一个代码示例相同的结果。

Answer 1

使用any：

v1, v2, v3, v4 = 0, 1, 1, 2

if any(x not in [0, 1] for x in [v1, v2, v3, v4]):
    print "bad"

当然，如果您使用列表，它看起来会更好

inputs = [1, 1, 0 , 2]

if any(x not in [0, 1] for x in inputs):
    print "bad"

Answer 2

这是由于python中的运算符优先级。 or运算符的优先级高于and运算符，列表如下所示：

or
and
not
!=，==

（资料来源：https://docs.python.org/3/reference/expressions.html#operator-precedence）

因此，python会像这样解释你的表达式（括号是为了澄清发生了什么）：

if (firstBinary != 0 or (firstBinary != 1 and secondBinary != 0 or (secondBinary != 1 and \
thirdBinary != 0 or (thirdBinary != 1 and forthBinary != 0 or (forthBinary != 1)))))

导致与您想要的逻辑不同。有两种可能的解决方案，第一种是添加括号以使表达式明确。这是相当乏味和冗长的：

if ((firstBinary != 0 or firstBinary != 1) and (secondBinary != 0 or secondBinary != 1) and \
(thirdBinary != 0 or thirdBinary != 1) and (forthBinary != 0 or forthBinary != 1))

另一种方法是使用内置的all函数：

vars = [firstBinary, secondBinary, thirdBinary, fourthBinary]
if not all(0 <= x <= 1 for x in vars):
    print("Only 0 or 1 allowed")

Answer 3

我将其细分为您试图解决的两个部分：

特定的输入是否有效？所有输入的部分是否都有效？

>>> okay = [0,1,1,0]
>>> bad = [0,1,2,3]

>>> def validateBit(b):
...    return b in (0, 1)

>>> def checkInput(vals):
...    return all(validateBit(b) for b in vals)
...
>>> checkInput(okay)
True
>>> checkInput(bad)
False
>>>

Answer 4

values = [firstBinary, secondBinary, thirdBinary]
if set(values) - set([0, 1]):
    print "Only 0 or 1, please"

验证几个变量的值

4 个答案: