“真，假”中的“0”返回True [英] "0 in [True,False]" returns True
问题描述
大家好，
在某些程序中，我测试变量是否为布尔值，使用此
测试：如果v in [True，False ]
我的脚本在某些情况下不起作用，我最终发现，对于v =
0，测试返回True
所以我改变了我的测试显而易见的如果类型（v）是bool，但我仍然
发现它混淆了0，真，假 ;返回True
顺便说一句，我在文档中搜索了obj in list中的内容。意味着和
无法找到一个精确的定义（它是否测试了相等性或
与列表中的一个值的身份？相等，似乎）;我没想错吗？
问候，
Pierre
Hi all,
In some program I was testing if a variable was a boolean, with this
test : if v in [True,False]
My script didn''t work in some cases and I eventually found that for v =
0 the test returned True
So I changed my test for the obvious "if type(v) is bool", but I still
find it confusing that "0 in [True,False]" returns True
By the way, I searched in the documentation what "obj in list" meant and
couldn''t find a precise definition (does it test for equality or
identity with one of the values in list ? equality, it seems) ; did I
miss something ?
Regards,
Pierre
推荐答案
Pierre Quentel写道：
Pierre Quentel wrote:
在某些程序中，我测试变量是否为布尔值，使用此测试：如果v in [True，错误]
我的脚本在某些情况下无法工作，我最终发现，对于v =
0测试返回True
所以我改变了我的测试对于明显的如果类型（v）是bool，但我仍然发现令人困惑的是0，在[真，假]中。返回True
顺便说一下，我在文档中搜索了obj in list中的内容。意味着并且
找不到一个精确的定义（它是否测试了与列表中的一个值之间的平等或
身份？似乎是相等的）;我是否错过了什么？
In some program I was testing if a variable was a boolean, with this
test : if v in [True,False]
My script didn''t work in some cases and I eventually found that for v =
0 the test returned True
So I changed my test for the obvious "if type(v) is bool", but I still
find it confusing that "0 in [True,False]" returns True
By the way, I searched in the documentation what "obj in list" meant and
couldn''t find a precise definition (does it test for equality or
identity with one of the values in list ? equality, it seems) ; did I
miss something ?
issubclass（bool，int）
True isinstance（False，int）
True False == 0
True int（False）
issubclass(bool, int) True isinstance(False, int) True False == 0 True int(False)
0
但是说真的，除非你正在编写一个内省工具，测试
bool是非常愚蠢的。只需使用if v即可或如果不是v，并将其余部分留给
Python。
< / F>
0
but seriously, unless you''re writing an introspection tool, testing for
bool is pretty silly. just use "if v" or "if not v", and leave the rest to
Python.
</F>
在星期一，2005-12-12 16:26，Pierre Quentel写道：
On Mon, 2005-12-12 at 16:26, Pierre Quentel wrote:
大家好，
在某些程序中我是测试一个变量是否是一个布尔值，用这个
测试：如果v in [True，False]
我的脚本在某些情况下不起作用，我最终发现对于v =
0测试返回True
所以我改变了我的测试显而易见的if type（v）bool，但我仍然觉得混淆了0在[真，假]中返回True
顺便说一下，我在文档中搜索了obj in list中的内容。意味着并且
找不到一个精确的定义（它是否测试了与列表中的一个值之间的平等或
身份？似乎是相等的）;我是否错过了什么？
Hi all,
In some program I was testing if a variable was a boolean, with this
test : if v in [True,False]
My script didn''t work in some cases and I eventually found that for v =
0 the test returned True
So I changed my test for the obvious "if type(v) is bool", but I still
find it confusing that "0 in [True,False]" returns True
By the way, I searched in the documentation what "obj in list" meant and
couldn''t find a precise definition (does it test for equality or
identity with one of the values in list ? equality, it seems) ; did I
miss something ?
您在哪里/如何搜索？ http://docs.python.org/lib/typesseq.html
毫不含糊地指出x in s返回如果s的项目是
等于x，则返回True，否则返回False
HTH，
Carsten。
Where/how did you search? http://docs.python.org/lib/typesseq.html
states unambiguously that "x in s" returns "True if an item of s is
equal to x, else False"
HTH,
Carsten.
Pierre Quentel写道：
Pierre Quentel wrote:
在某些程序中，我测试变量是否为布尔值，使用此
测试：如果v in [True，False]
我的脚本在某些情况下不起作用，我最终发现，对于v =
0，测试返回True
In some program I was testing if a variable was a boolean, with this
test : if v in [True,False]
My script didn''t work in some cases and I eventually found that for v =
0 the test returned True
这似乎是一个奇怪的测试。这段代码试着做什么？
如果你确定你必须这样做，我会做到：
如果isinstance（v，bool）：
...
或
如果v为True或v为错误：
...
但看起来这段代码似乎正在尝试用Python编写其他语言代码
。 ..
STeVe
This seems like a strange test. What is this code trying to do?
If you''re sure you have to do this, I would do either:
if isinstance(v, bool):
...
or
if v is True or v is False:
...
But it really seems like this code is trying to code some other language
in Python...
STeVe
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