++
is not an operator. It is two +
operators. The +
operator is the identity operator, which does nothing. (Clarification: the +
and -
unary operators only work on numbers, but I presume that you wouldn't expect a hypothetical ++
operator to work on strings.)
++count
Parses as
+(+count)
Which translates to
count
You have to use the slightly longer +=
operator to do what you want to do:
count += 1
I suspect the ++
and --
operators were left out for consistency and simplicity. I don't know the exact argument Guido van Rossum gave for the decision, but I can imagine a few arguments:
- Simpler parsing. Technically, parsing
++count
is ambiguous, as it could be +
, +
, count
(two unary +
operators) just as easily as it could be ++
, count
(one unary ++
operator). It's not a significant syntactic ambiguity, but it does exist.
- 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.
- Confusing side-effects. One common newbie error in languages with
++
operators is mixing up the differences (both in precedence and in return value) between the pre- and post-incremend/decrement operators, and Python likes to eliminate language "gotcha"-s. The precedence issues of pre-/post-increment in C are pretty hairy, and incredibly easy to mess up.