Suggestion for "syntax error": ++i, --i

[Petr Prikryl]

Hi,

Summary: In my opinion, the C-like prefix
increment and decrement operators (++i and --i)
should be marked as "syntax error".


Current situation: try... (Python 2.4 (#60, ...))
>>> i = 1
>>> i
1
>>> i++
  File "<stdin>", line 1
    i++
      ^
SyntaxError: invalid syntax
>>> ++i
1
>>> --i
1
>>>

Reason for how ++i and --i behaves in Python is 
that it is probably treated as (-(-i)) and (+(+i))
respectively.

Rationale: My guess is that many Python users
do use other languages at the same time. 
The C-family languages do use the prefix increment
and decrement operators. When used in Python
no warning appears -- the code simply does not work
as expected. In the same time, there is probably no
reason to use the increment and decrement 
prefix operators. On the other hand, the newcommer
or the programmer that "types ++i automatically 
because of brain synapses say he/she should..."
is not warned until something does not work.

Con: The situation must be recognized by the parser
(i.e. someone have to implement it).

Pro: No runtime overhead except of the detection
of the situation. As Python is a good candidate
to be used as the language for teaching, the "syntax
error" would be the pedagogical plus.

Personal experience: Many things in Python work
intuitively. My C++ experience "forced me" to use
++i as described above. I use iteration more these
days and I know about the ++i problem invisibility 
in Python. But I had to learn by mistake. The ++i
behaviour is not intuitive for me.

Your opinion?


-- 
Petr Prikryl (prikrylp at skil dot cz)