On 1 Jan 2014 10:33, "PJ Eby" wrote:

On Sat, Dec 21, 2013 at 9:46 AM, Nick Coghlan wrote:

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I've just published the first draft of the metadata 2.0 spec that moves all of the fields that aren't part of the core metadata or potentially needed for dependency resolution out to a separate "standard metadata extensions" PEP.

Yay!

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I think this makes PEP 426 itself substantially less overwhelming, and also provides convenient names to refer to the various other subsets of the metadata.

Indeed!

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Metadata 2.0: http://www.python.org/dev/peps/pep-0426/ Versioning: http://www.python.org/dev/peps/pep-0440/ Standard Extensions: http://www.python.org/dev/peps/pep-0459/

I have only been skimming these so far, will comment more later, but I just want to mention that for standard extensions, what is the rationale for not defining e.g. commands as exports? Or for that matter, defining hooks as exports? Both commands and hooks have a payload that's the same as an export payload, i.e., a reference to an importable object. I think it'd be good for them to be defined in terms of exports in order to reduce duplication of concepts and implementations, as well as providing a PEP-defined example of how to use export groups and export names effectively.

I believe it was due to the extra layer of nesting they needed - using multiple parallel export groups with different final elements in their dotted names didn't feel right. I guess that indicates a flaw in my initial design for the export definitions though - I agree it would be better if commands and hooks could be cleanly defined within the exports mechanism, rather than needing separate custom metadata extensions. I'll take another look at using either parallel export groups, or else allowing subdivision of export groups as a general feature.

(Also, noting the mapping of current script export namespaces to the new metadata would be helpful for people implementing translation tools from setuptools metadata.)

Last but not least, some of the export examples should use dotted post-module names (e.g. "some.module:RandomClass.a_class_method") to highlight that qualified names can be used there. (Yes, the spec *says* qualified names, but it's the sort of thing that people overlook when the examples are all of unqualified simple names.)

Yeah, those are both good ideas. Cheers, Nick.

On Wed, Jan 1, 2014 at 9:39 AM, Nick Coghlan wrote:

On 1 Jan 2014 10:33, "PJ Eby" wrote:

...

I have only been skimming these so far, will comment more later, but I just want to mention that for standard extensions, what is the rationale for not defining e.g. commands as exports? Or for that matter, defining hooks as exports? Both commands and hooks have a payload that's the same as an export payload, i.e., a reference to an importable object. I think it'd be good for them to be defined in terms of exports in order to reduce duplication of concepts and implementations, as well as providing a PEP-defined example of how to use export groups and export names effectively.

I believe it was due to the extra layer of nesting they needed - using multiple parallel export groups with different final elements in their dotted names didn't feel right.

I guess that indicates a flaw in my initial design for the export definitions though - I agree it would be better if commands and hooks could be cleanly defined within the exports mechanism, rather than needing separate custom metadata extensions.

If it's a flaw, I'd say it's in my original design of entry points. ;-) Basically, I wanted a way to do -- without XML -- what Eclipse does with its "extensions" and "extension points" machinery. I went with a "flat (with dots) is better than nested" concept. To me, though, this doesn't look terribly complicated (using entry points syntax): [python.exports.after_install] ComfyChair.plugins = ComfyChair.plugins:install_hook [python.exports.after_uninstall] ComfyChair.plugins = ComfyChair.plugins:install_hook Nor this: [python.extensions.after_install] python.exports = pip.export_group_hooks:run_install_hooks python.commands = pip.command_hook:install_wrapper_scripts [python.extensions.after_uninstall] python.exports = pip.export_group_hooks:run_uninstall_hooks (Also, adding hooks to *validate* extensions and exports at build and/or install time might be handy.) Finally, note that if the typical usecase is to define *both* an install and uninstall hook, then it might be simpler to just define the hook once, as an object with 'after_install' and 'after_uninstall' methods. This avoids the need to register a hook in two groups, and in the simplest case people can just make them both module-level functions and list the module as the export.