On 18/10/06, David Cournapeau <[EMAIL PROTECTED]> wrote: > Sven Schreiber wrote: > > > > Yes it's intended; as far as I understand the python/numpy syntax, <+> > > is an operator, and that triggers assignment by copy (even if you do > > something trivial as bar = +foo, you get a copy, if I'm not mistaken), > > > So basically, whenever you have > > foo = expr > > with expr is a numpy expression containing foo, you trigger a copy ?
No. "=" never copies, but "+" does: when you do "A+B" you produce a new, freshly-allocated array, which you can then store (a reference to) in any variable you like, including A or B. So M = M+1 makes a copy because "M+1" is a new matrix, which you are assigning to M. Unfortunately, this means if you do: M = 2*(M+1) python makes the new matrix M+1, then makes the new matrix 2*(M+1), discards M+1, and sets M to point to 2*(M+1). If you want to avoid all this copying, you can use python's in-place operators: M += 1 M *= 2 This is actually a standard difficulty people have with python, made more obvious because you're working with mutable arrays rather than immutable scalars. A. M. Archibald ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ Numpy-discussion mailing list Numpy-discussion@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/numpy-discussion
