在python中，++ x是正确的语法。


in python, ++x is correct syntax. What does “++x” mean?

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Possible Duplicate:
Python: Behaviour of increment and decrement operators

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

为什么++X可以？

(我问的是，因为工作中的某个人习惯性地写了++I，这并没有(习惯性地)预期的那样做，但也没有抛出错误，所以花了一些时间才发现错误。)

相关讨论

它的意思是+(+a)，即与-(-a)的意思相反(虽然在这种情况下，结果显然是相同的！)

请参见http://docs.python.org/library/stdtypes.html numeric types int float long complex。

相关讨论

相当于+(+a)：

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

python的可能副本：递增和递减运算符的行为。

虽然我找不到有关操作员确切推理的文件，但我将引用我认为是这种情况的关联问题中已接受答案的一部分：

  • 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.