args, key=value pairs and task yaml

[Tim Flink]

On Wed, 5 Feb 2014 05:43:16 -0500
Ralph Bean <rbean at redhat.com> wrote:

> On Tue, Feb 04, 2014 at 02:02:42PM -0700, Tim Flink wrote:
> >  ---- SNIP ----
> >
> > What I'm looking to decide is whether we really need args in
> > addition to of key=value pairs and if the added complexity is worth
> > it.
> > 
> > I propose that we alter the format to use only key=value pairs which
> > would be parsed into a dict in the runner. Using the same example as
> > above, the new action would look something like:
> > 
> > ------------------------------------------------------------
> > Execution:
> >     python: pyfile=runtask.py method_name=do_something action=fix
> > ------------------------------------------------------------
> > 
> > This would simplify the parsing code and the data passing logic for
> > execution since all input data would be in the form of a dictionary
> > instead of separated out into a list/string and a dictionary.
> > 
> > While I slightly prefer the aesthetics of allowing one or more
> > keyless args in an action instead of all key=value pairs, I can't
> > think of a use case where restricting input to key=value pairs
> > would cause problems.
> > 
> > If we do decide that keyless args are needed, I'd rather support
> > more than one instead of the current arbitrary restriction of just
> > one arg.
> > 
> > Any other thoughts?
> > 
> > Tim
> 
> How about something like this:
> 
> ------------------------------------------------------------
> Execution:
>     python:
>         file: runtask.py
>         method: do_something
>         args:
>         - first_positional_arg
>         - second_positional_arg
>         kwargs:
>             action: fix
> ------------------------------------------------------------
> 
> It takes many more lines to express a task, but the indentation shows
> structure and it is much more flexible.  Perhaps it is overkill?

It's certainly easier to read for more complex actions and does make it
easier to pass in stuff like lists. For the python directive, it also
makes the treatment of args and kwargs passed into the python callable
much more explicit.

The only concern I have is that it requires a bit more knowledge of how
yaml works and is parsed. For example, the difference between

------------------------------------------------------------
args:
  - first_positional_arg
  - second_positional_arg
------------------------------------------------------------

and

------------------------------------------------------------
args:
  first_positional_arg
  second_positional_arg
------------------------------------------------------------

The first is parsed as a list (['first_positional_arg',
'second_positional_arg']) and the second is parsed as a space delimited
string ('first_positional_arg second_positional_arg'). I'm not sure how
we could check for validity on a generic basis since there are valid
uses for both parsed forms.

Either way, I think that it makes sense to do away with the
non-key-value inputs. Now the question becomes what format the actions
should take.

For a larger example, let's look at an excerpt from rpmlint. This is an
example of what a set of actions could look like using key=value pairs
and not taking advantage of many yaml structures.

-----------------------------------------------------------
    - name: download rpms from koji
      koji: action=download envr={{ envr }}

    - name: run rpmlint on downloaded rpms
      python: file=run_rpmlint.py workdir={{ workdir }}
      register: rpmlint_output

    - name: report results to resultsdb
      resultdb: results={{ rpmlint_output }}
-----------------------------------------------------------

It's somewhat dense but for this example, it's not that difficult to
read.

For an example with the structures mentioned above:

------------------------------------------------------------
Execution:
    - name: run createrepo
      createrepo:
          action: create
          dir: "{{workdir}}/somedir"

    - name: run rpmlint on downloaded rpms
      python:
          file: run_rpmlint.py
          workdir: "{{ workdir }}"
      register: rpmlint_output

    - name: report results to resultsdb
      resultdb:
          results: "{{ rpmlint_output }}"
-----------------------------------------------------------

There are some changes to the way that the actions are represented but
it's much easier for my human eyes to parse the actions since it's
effectively limited to one input per line.

I'm kind of partial to the second form, myself. Any other thoughts?

Tim
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