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
why ++x is OK?
(I'm asking since someone at work habitually wrote ++i, which didn't do as (habitually) expected, but didn't throw an error either, so it took some time to find the bug.)
It means +(+a), i.e. opposite to the meaning of -(-a) (although obviously in this case, the result is the same!)
See http://docs.python.org/library/stdtypes.html#numeric-types-int-float-long-complex.
+(+a) actually is not the opposite of -(-a), it's the same :-)
It is equivalent to +(+a):
>>> +-2
-2
>>> -+2
-2
>>> --2
2
>>> ++++-2
-2
Possible duplicate of Python: Behaviour of increment and decrement operators.
Although I cannot find documentation for the exact reasoning for the operator I'll quote a portion from the accepted answer in the linked question that I believe is the case:
- 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.
