Robert Kern wrote:
On Thu, Mar 12, 2009 at 17:45, Sturla Molden <sturla@molden.no> wrote:
2009/3/13 Charles R Harris <charlesr.harris@gmail.com>:
That said, I think it best to leave '%' with its C default and add a special modulus function for the python version. Changing its meaning in C-like code is going to confuse things. This is Cython code, so I think there is an argument to be made that it is Python-like!
I'll just repeat what I've already said on the Cython mailing list:
I think C types should behave like C types and Python objects like Python objects. If a C long suddenly starts to return double when divided by another C long, then that will be a major source of confusion on my part. If I want the behaviour of Python integers, Cython lets me use Python objects. I don't declare a variable cdef long if I want it to behave like a Python int.
Whether division returns float or not is an orthogonal and unrelated issue (and when it does, which is not the default, // is the C division operator). When we say that this affects division; what we mean is that -7 // 6 returns -2 in Python; so that (-7 // 6)*6 + (-7 % 6) == -2*6 + 5 == -7. With C behaviour of % and /, I believe -7 // 6 == -1. (And when I use // it is to be unambigious; by default you can use / as well for the same thing.)
That may be part of the confusion. The expression "-1%5" has no variables. Perhaps Dag can clarify what he is asking about:
# Constants? (No one uses just constants in expressions, # really, but consistency with the other choices will # affect this.) -1 % 5
# Explicitly declared C types? cdef long i, j, k i = -1 j = 5 k = i % j
This one is what I'm really asking about.
When I do (2147483647 + 2147483647) in current Cython, to choose another operation, does it use C types, or does it construct PyInts? I.e., do I get C wraparound arithmetic, or do I get a PyLong?
C wraparound. Suggestions welcome :-)
I recommend making % behave consistently with the other operators; i.e. if <x>+<y> uses C semantics, <x>%<y> should, too.
-- Dag Sverre