Python '+=' 和 '==+' 的区别？
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The difference between '+=' and '=+'?
提问by faceless
So I have a simple piece of code that prints out the integers 1-10:
所以我有一段简单的代码可以打印出整数 1-10：
i = 0
while i < 10:
i += 1
print(i)
Then if you just change one operator around on line 3, it prints out an infinite amount of 1 integers(which i understand why it does that). Why isn't a syntax error occurring when running this second program? Wouldn't it call a syntax error in the event of an assignment operator being followed by an addition operator??
然后，如果您只是在第 3 行更改一个运算符，它会打印出无限数量的 1 个整数（我明白为什么要这样做）。为什么在运行第二个程序时没有发生语法错误？如果赋值运算符后跟加法运算符，它不会调用语法错误吗？？
i = 0
while i < 10:
i =+ 1
print(i)
回答by Kittsil
i+=1is the same as i=i+1, whereas
i=+1just means i=(+1).
i+=1与 相同i=i+1，而
i=+1只是意味着i=(+1)。
回答by ShadowRanger
Tokenizers don't typically require spaces unless it's necessary to disambiguate (e.g. you need a space, or punctuation of some form between a variable name and a language keyword so the keyword can be recognized).
分词器通常不需要空格，除非有必要消除歧义（例如，您需要一个空格，或变量名和语言关键字之间的某种形式的标点符号，以便可以识别关键字）。
Thus, x=+y, x =+ yand x = +yare all equivalent, in all cases invoking the unary +operator on yand assigning to x. The unary plus operator isn't commonly used, but just because it's uncommon doesn't mean it's not recognized and accepted.
因此，x=+y，x =+ y和x = +y都是等价的，在调用一元所有情况下+运营商y和分配到x。一元加号运算符并不常用，但仅仅因为它不常见并不意味着它不被认可和接受。
For comparison, the -->"operator" in C/C++ etc. is another example where humans looking for spaces and tokenizers ignoring them causes confusion.
相比之下，-->C/C++ 等中的“运算符”是另一个示例，其中人类寻找空格而标记器忽略它们会导致混淆。
回答by Ned Batchelder
i =+ 1is the same as i = +1, or i = 1.
i =+ 1与i = +1, 或相同i = 1。
回答by Mercury
x=+1is treated as: x=(+1)
while x+=1is treated as: x=x+1
x=+1被视为： x=(+1)
而x+=1被视为：x=x+1
There are binary operators which operates on their left-handside operand and their right-hand side operand (e.g. * multiplication).
And there are unary operators which takes only right-hand side operand (e.g. ~/! negation).
There are operators which can be unary and binary.
有一些二元运算符对它们的左侧操作数和右侧操作数进行操作（例如 * 乘法）。
还有一元运算符只接受右侧的操作数（例如 ~/! 否定）。有可以是一元和二元的运算符。
The plus sign in python can be used also as right-hand side operator just as minus.
python 中的加号也可以用作右侧运算符，就像减号一样。
Python Docs:
Python 文档：
The unary - (minus) operator yields the negation of its numeric argument.
The unary + (plus) operator yields its numeric argument unchanged.
一元 -（减号）运算符产生其数字参数的否定。
一元 +（加号）运算符产生其数值参数不变。
回答by Fantastic Mr Fox
There is no syntax error because the expression i =+ 1is the same as i = (+1)and +1is perfectly legitimate. It is a unary operator, not the addition operator.
没有语法错误，因为表达式i =+ 1与完全相同i = (+1)并且+1完全合法。它是一元运算符，而不是加法运算符。
