与无比较 [英] comparison with None

问题描述

>>无> = 0

错误

>>无< = 0

True


说明赞赏。


谢谢，

Alan Isaac

解决方案

" Alan G Isaac" < ai **** @ american.eduwrote in message

news：3I ************************** **** @ rcn.net ...

| >>无> = 0

|错误

| >>无< = 0

|真的

|

|感谢解释。


应该在比较的参考手册部分。

Alan G Isaac写道：

>>无> = 0

False

>>无< = 0

True


说明赞赏。


谢谢，

Alan Isaac

我读过并发现''无'比较并不总是一个好主意。

更好to：

from types import NoneType


x = None

如果type（x）== NoneType：

＃true

<代码>

else：

#false;做其他事情。

<更多代码>


Steven Howe

4月18日下午5:19，Steven Howe< howe.ste ... @ gmail.comwrote：

Alan G Isaac写道：

>>无> = 0

错误

> >无< = 0

True

说明赞赏。

谢谢，

Alan Isaac

我'已经阅读并发现''无'比较并不总是一个好主意。

最好：

来自类型进口NoneType


x =无

如果类型（x）== NoneType：

＃true

<代码>

else：

#false;做其他事情。

<更多代码>


Steven Howe

没有单身 - 只有一个没有，没有其他。与None无关的唯一

比较是是。或不是。 type（x）

== NoneType是不必要的，x是None就足够了。

>> x =无
x为无

True
< blockquote class =post_quotes>

>> y =无
x是y

True

> > z = object（）
z是无

False

>> z不是无

True

>> x不是无

False

>> y不是无

False


- Paul

>>None >= 0
False

>>None <= 0

True

Explanation appreciated.

Thanks,
Alan Isaac

解决方案

"Alan G Isaac" <ai****@american.eduwrote in message
news:3I******************************@rcn.net...
| >>None >= 0
| False
| >>None <= 0
| True
|
| Explanation appreciated.

Should be in the reference manual section on comparisons.

Alan G Isaac wrote:

>>None >= 0

False

>>None <= 0

True

Explanation appreciated.

Thanks,
Alan Isaac

I''ve read and found that ''None'' comparisons is not always a good idea.
Better to:
from types import NoneType

x = None
if type( x ) == NoneType:
# true
< code >
else:
# false; do something else.
< more code >

Steven Howe

On Apr 18, 5:19 pm, Steven Howe <[e-mail]:

Alan G Isaac wrote:

>>None >= 0

False

>>None <= 0

True

Explanation appreciated.

Thanks,
Alan Isaac

I''ve read and found that ''None'' comparisons is not always a good idea.
Better to:
from types import NoneType

x = None
if type( x ) == NoneType:
# true
< code >
else:
# false; do something else.
< more code >

Steven Howe

None is a singleton - there is but one None and no other. The only
comparisons that make sense with None are "is" or "is not". type(x)
== NoneType is unnecessary, x is None is sufficient.

>>x = None
x is None

True

>>y = None
x is y

True

>>z = object()
z is None

False

>>z is not None

True

>>x is not None

False

>>y is not None

False

-- Paul

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