Re: Question about (properties `((python2-variant . , (delay XXX)))) and name resolution

[Ricardo Wurmus <ricardo.wurmus@mdc-berlin.de>]

Danny Milosavljevic <dannym@scratchpost.org> writes:

> Hi Leo,
>
> On Tue, 19 Jul 2016 23:58:23 -0400
> Leo Famulari <leo@famulari.name> wrote:
>
>> In this case, it looks like the Python 2 variant of the package is the
>> same as the Python 3 variant, aside from the Python version. So, you
>> should be able to drop the (properties `((python2-variant ...) line from
>> the python-ptpython package.
>
> I tried that, but I still can't do
>
>   $ guix package -i ptpython-2
>
> because:
>
>   guix package: error: ptpython: package not found for version 2

What you wrote there is the old way of asking Guix to install a
particular *version* of a package.  This has been changed to “@” some
time ago.

This means that you are asking Guix to install a package named
“ptpython” with package version “2” (not Python version 2), but no such
package exists — you only defined two variants of a package with version
0.34.

Our policy with Python *modules* is to prefix them with “python-” or
“python2-”.  When you define the Python 3 variant as “python-ptpython”
and give it the name “python-ptpython” then “package-with-python2” will
take care of renaming this to “python2-ptpython” for the Python 2
variant.

(For packages that only provide executables we usually don’t add the
prefix.)

> Now, the ptpython executables are still called the same - so you can't
> install ptpython and ptpython-2 at the same time.

Ah, an executable.  If this is not to be used as a library/module does
it even make sense to build it with different versions of Python?  If
all you care about is the executables then having a variant with only
the latest version of Python seems sufficient.  (We do the same for
snakemake, for example.)

~~ Ricardo