[bug#68416] [PATCH] python: add 3.20 - 3.16 to the version search list

Frederic Berat wrote:
> On Sun, Jan 14, 2024 at 3:13 AM Karl Berry <[email protected]> wrote:
>
>   
>>     With Python 3.12 out now, and 3.13 out in ~9 months, the existing
>> runway
>>     is running out.  Bump up to 3.20 for the next Automake release.
>>
>> Applied, thanks.
>>
>> Not proposing to try anything for our upcoming release, but I wonder if
>> there is some more general way to handle Python versions? We don't have
>> to laboriously list every possible version for anything else.
>>
>>     
>
> That may not be the most clever way to do it, but you can probably build
> the list dynamically at least, with something like (untested):
>
> pythons="python python2 python3"
> for i in {20..0};do pythons="$pythons python3.$i";done
> for i in {7..0};do pythons="$pythons python2.$i";done
>
> m4_define_default([_AM_PYTHON_INTERPRETER_LIST], [$pythons])
>   

The {20..0} is a syntax unfamiliar to me, yet even Bash 3 has it... 
interesting.  Also interesting that it is brace expansion, so you could do:

pythons=`echo python{,2,3} python3.{20..0} python2.{7..0}`

The use of command substitution and echo works around the small catch 
that brace expansion does not occur inside double quotes.  However, 
brace expansion does occur inside a command substitution inside double 
quotes, but the result of command substitution as a variable assignment 
is not subject to word splitting, so the double quotes can be omitted.  
I wonder if all shells that allow {20..0} also allow $() for command 
substitution, or if this code must be valid in shells that predate POSIX...

Oh wait, after reviewing the thread, I find that this is in m4 macros.  
Yes, it could be dynamically produced, but not using shell iteration 
constructs or expansions.  Macros in m4 are allowed to use tail 
recursion, and counted iteration is possible to implement (and autoconf 
provides some macros for it).

The required quoting is "fun" and Automake may complain that this 
appears to be underquoted:  (untested; the fine details of the quoting 
may be wrong)

m4_define_default([_AM_PYTHON_INTERPRETER_LIST],  dnl
    [python python2 python3] dnl
    m4_for(i, 20, 0, -1, [ python3.i]) dnl
    m4_for(i, 7, 0, -1, [ python2.i]))

As written, this might lead to some extra spaces in the interpreter 
list, but the shell will ignore those when running configure.


-- Jacob