On Sat, Jan 26, 2013 at 2:18 PM, Allin Cottrell <cottrell@wfu.edu> wrote:

On Sat, 26 Jan 2013, Pietro Battiston wrote:

> I love Gretl's "foreign" code blocks capability, and would love even
> more the possibility of using Python in them, which was at some time
> suggested as easy to implement.

Yes, quite easy. In fact, so easy that Python support is now
in gretl CVS and the snapshots for Windows and OS X. Here's a
trivial example:

Cool. Thanks. Is there any way to browse this changeset in the repository through the web interface? Git/github has eroded all of my other version control skills.

Nevermind. I see it in my local checkout.

<hansl>
matrix M = I(5)
mwrite(M, "@dotdir/pytest.mat")
foreign language=python
G = gretl_loadmat('pytest.mat')
G *= 5
gretl_export(G, 'pyout.mat')
end foreign
matrix pymat = mread("@dotdir/pyout.mat")
print pymat
</hansl>

When you call python via gretl's "foreign" mechanism you have
three gretl_ functions available:

gretl_loadmat(): reads a matrix, as written by gretl's
mwrite(), from gretl's per-user dotdir.

gretl_export(): writes a matrix, readable via gretl's mread(),
into the gretl dotdir.

gretl_dotdir(): in case you need it, gives the dotdir path.

When python is invoked via gretl, one thing that happens
automatically is:

import numpy as np

This is in part because numpy is needed for the implementation
of gretl_loadmat and gretl_export, which use np.loadtxt and
np.savetxt respectively. I'm not a python person, but I
suspect that some users might not like the "import" statement
as I have it. Comments welcome.

This is the preferred import convention for numpy, so there's no reason to not like it from a style standpoint. Are you concerned with this or the importing the kitchen sink aspect?

Related question: in Python, as in R, Octave and Ox, the
"dotdir" business (which ensures we have a user-writable and
gretl-findable location) is hidden from the matrix read/write
functions, but on the gretl end you have to use @dotdir
explicitly with mwrite and mread when interfacing with
"foreign".

Any sale for a pair of gretl functions mexport() and mimport()
which handle the prepending of dotdir automatically?

Allin Cottrell

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