PYPKGPREFIX or _PYTHON_VERSION to include dependencies per-Python? (was: Re: CVS commit: pkgsrc/www/py-urllib3)

[Leonardo Taccari <leot%NetBSD.org@localhost>]

Hello Adam and all pkgsrc-changes@ folks!
I'm just curious about that (AFAIK in pkgsrc we do not do that
consistently and both ways are used).

"Adam Ciarcinski" writes:
> Module Name:  pkgsrc
> Committed By: adam
> Date:         Thu Sep  6 13:43:18 UTC 2018
>
> Modified Files:
>       pkgsrc/www/py-urllib3: Makefile
>
> Log Message:
> py-urllib3: fix py-ipaddress dependency
>
> [...]
> Index: pkgsrc/www/py-urllib3/Makefile
> diff -u pkgsrc/www/py-urllib3/Makefile:1.8 pkgsrc/www/py-urllib3/Makefile:1.9
> --- pkgsrc/www/py-urllib3/Makefile:1.8        Sat Jun 16 12:10:40 2018
> +++ pkgsrc/www/py-urllib3/Makefile    Thu Sep  6 13:43:18 2018
> [...]
> @@ -15,7 +15,9 @@ DEPENDS+=   ${PYPKGPREFIX}-Socks>=1.6.0:..
>  DEPENDS+=    ${PYPKGPREFIX}-certifi-[0-9]*:../../security/py-certifi
>  DEPENDS+=    ${PYPKGPREFIX}-cryptography>=1.3.4:../../security/py-cryptography
>  DEPENDS+=    ${PYPKGPREFIX}-idna>=2.0.0:../../www/py-idna
> -.if "${PYPKGPREFIX}" == "py27"
> +
> +.include "../../lang/python/pyversion.mk"
> +.if ${_PYTHON_VERSION} == 27
>  DEPENDS+=    ${PYPKGPREFIX}-ipaddress-[0-9]*:../../net/py-ipaddress
>  .endif

Why use ${PYPKGPREFIX} or ${_PYTHON_VERSION}?