在python中，++x是正确的语法。“++x”是什么意思？

Question

Possible Duplicate:
Python: Behaviour of increment and decrement operators

>>> a=2
>>> ++a
2
>>> a++
Traceback (  File "<interactive input>", line 1
    a++
      ^
SyntaxError: invalid syntax
>>> ++a
2

为什么++x可以？在

（我之所以问这个问题，是因为工作中有人习惯性地编写了++I，这并不像（习惯性地）期望的那样，但也没有抛出错误，所以花了一些时间才找到错误。）

Answer 1

可能是Python: Behaviour of increment and decrement operators的重复项。在

虽然我找不到操作人员确切推理的文档，但我将引用链接问题中已接受答案的一部分，我认为是这样：

• Simpler language. ++ is nothing more than a synonym for += 1. It was a shorthand invented because C compilers were stupid and didn't know how to optimize a += 1 into the inc instruction most computers have. In this day of optimizing compilers and bytecode interpreted languages, adding operators to a language to allow programmers to
  optimize their code is usually frowned upon, especially in a language like Python that is designed to be consistent and readable.

Answer 2

它相当于+(+a)：

>>> +-2
-2
>>> -+2
-2
>>>  2
2
>>> ++++-2
-2

Answer 3

它的意思是+(+a)，即与{}的意思相反（尽管在这个例子中，结果显然是一样的！）在

见http://docs.python.org/library/stdtypes.html#numeric-types-int-float-long-complex。在