为什么= =（而不仅仅是=） [英] Why = = (and not just =)
问题描述
抱歉，我无法帮助解决愚蠢的问题：
我明白为什么我们需要= =在C中，但为什么在Python（或Java）中，
当然如果你写了
如果a = b：传递＃语法错误
它不可能意味着除了我想要的任何东西
（当然如果a = = b :)？
Sorry, I cant help aking stupid questions:
I understand why we need = = in C, but why in Python (or Java),
surely if you write
if a=b: pass # syntax error
it could not possibly mean anything other than what I intended
(which was of course if a = = b:) ?
推荐答案
Joe Green写道：
Joe Green wrote:
抱歉，我无法帮助愚蠢的问题：
我理解为什么我们需要= =在C中，但为什么在Python（或Java）中，
如果你写的话肯定是
如果a = b：传递＃语法错误
它不可能意味着我想要的东西
（当然，如果a = = b :)？
Sorry, I cant help aking stupid questions:
I understand why we need = = in C, but why in Python (or Java),
surely if you write
if a=b: pass # syntax error
it could not possibly mean anything other than what I intended
(which was of course if a = = b:) ?
当然，人们可以使用=。表示相等的测试。
但是，我相信这个语法是从ABC继承而来的，它可能是从B继承的。另外，它*是*有用的
在语法上区分赋值和相等测试
即使解析器不需要这样的区别：人类读者可能会被骗到b $ b什么东西都不存在。
问候，
马丁
Certainly, one could have use "=" to denote the test for equality.
However, I believe that this syntax was inherited from ABC, which
probably inherited it from C. In addition, it *is* useful to
syntactically distinguish between assignments and equality tests
even if the parser does not need that distinction: The human reader
might be tricked into seeing something that isn''t there.
Regards,
Martin
Joe Green写道：
Joe Green wrote:
抱歉，我无法帮助解决愚蠢的问题：
我理解为什么我们需要= =在C中，但为什么在Python（或Java） ），
肯定如果你写了
如果a = b：传递＃语法错误
它不可能意味着除了我想要的任何东西
（当然，如果a = = b :)？
Sorry, I cant help aking stupid questions:
I understand why we need = = in C, but why in Python (or Java),
surely if you write
if a=b: pass # syntax error
it could not possibly mean anything other than what I intended
(which was of course if a = = b:) ?
我不是特别喜欢它，但你可以链接作业：
I don''t particularly like it, but you can chain assignments:
b = 1
a = b = 2
a，b
（2,2）
a = b = = 2
a，b
（真，2）
b = 1
a = b = 2
a,b (2, 2)
a = b == 2
a,b (True, 2)
HTH，
Peter
HTH,
Peter
>>>>> 乔格林 <所以***** @ microsoft.com> （JG）写道：
JG>对不起，我无法帮助解决愚蠢的问题：
JG>我理解为什么我们需要= =在C中，但为什么在Python（或Java）中，
JG>当然，如果你写的是
JG>如果a = b：传递＃语法错误
JG>它不可能意味着我想要的任何东西
JG> （当然，如果a = = b :)？
那么a = b = c与a = b == c怎么样？
-
Piet van Oostrum< pi ** @ cs.uu.nl>
网址： http://www.cs.uu.nl/~piet [PGP]
私人电子邮件： P.***********@hccnet.nl
>>>>> "Joe Green" <so*****@microsoft.com> (JG) wrote:
JG> Sorry, I cant help aking stupid questions:
JG> I understand why we need = = in C, but why in Python (or Java),
JG> surely if you write
JG> if a=b: pass # syntax error
JG> it could not possibly mean anything other than what I intended
JG> (which was of course if a = = b:) ?
So what about a = b = c vs. a = b==c?
--
Piet van Oostrum <pi**@cs.uu.nl>
URL: http://www.cs.uu.nl/~piet [PGP]
Private email: P.***********@hccnet.nl
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