[PYTHON MATRIX-SIG] A related idea
Thu, 9 Nov 1995 11:10:44 -0800
Jim Hugunin replied, in response to my suggestion for providing an
"adoption" method for compiled arrays:
> Suppose we have the matrix class working.
What do you mean suppose ;) ?
Hey, I'm a mathematician, all my sentences start with suppose!
> Suppose there is a Fortran
> or C array in the program which you would like to "adopt" as a
> matrix in Python. The only difference between this and a matrix created a
> normal way is that you have to remember never to free the memory.
> So it seems you might be able to do this if you had a method
> of creation (from C) which took a pointer,size,type kind of
> description. You could then increment the reference counter one extra, so
> that the memory is never freed, or a "don't free" flag could be in the
I agree that there should be a function to create a new matrix object from
an existing array in C (or FORTRAN). What we disagree about is the
semantics. I played around a while with the idea of "sharing" an array
between python and C. I found that as a general rule I ran into memory leak
problems (or worse). Using your scheme, python is never responsible for
freeing the allocated memory, this means that the C code must be responsible
for it, but the C code can't know when it is safe to free the memory
because even when it's done with it there might still be a python reference
to the memory.
Let me know if I'm completely missing something here, and this memory leak
issue isn't really a problem.
This is a good point which I hadn't thought of because the way I intend to
use this "adopting" the arrays are the permanent state of a calculation and
are never "released" by the compiled code. I was aware that if I wanted to
ever change size etc. I would somehow need to tell Python about it. Some
careful thinking is required in that case.
The point isn't that I want to save memory but that I want to MODIFY the
array the compiled code is using, such as an array in a Fortran common block.
I don't have a problem copying it when I'm going to do something with it.
But to use it as a method of input to a code, I need to be able to do
import phys1 #load up physics code
phys1.x = <matrix expression>
phys1.x = 1.
Here I'm assuming x is created by the initialization of the module such
that it has the "real" x in the compiled code as a data area.
Obviously, one could instead provide methods (e.g., set_x, set_y, set_z)
but it dispels the illusion that x is really a matrix attribute of a physics
Maybe I'm not taking the right approach here. Suggestions appreciated.
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