[Distutils] entry points PEP

[Daniel Holth]

On Thu, Jul 18, 2013 at 1:50 PM, Vinay Sajip <vinay_sajip at yahoo.co.uk> wrote:
> Daniel Holth <dholth <at> gmail.com> writes:
>
>> On Thu, Jul 18, 2013 at 9:27 AM, Paul Moore <p.f.moore <at> gmail.com>
> wrote:
>
>> It is an extension so it can be a separate PEP, since there's enough
>> to talk about in the main PEP. The document tries to write down what
>> setuptools does in a straightforward json way.
>
> If the JSON we're talking about goes in the main metadata dictionary,
> perhaps
> it should go into PEP 426, so that everything is in one place. As we're
> talking
> about special handling of script generation by installers, it may make sense
> to
> not consider them as extensions but as core metadata.
>
>> > 2. distlib calls these "exports" and I think that's a better name. But
> if
>> > names are all that we argue over, I'm happy
>
> The reason for picking "exports" is that you can export data, not just code,
> and "entry point" has a connotation of being code. PJE suggested "exports"
> and
> I think it fits the bill better than "entry_points".
>
>> > 3. Someone (I think it was PJE) pointed out that having entry points in
> a
>> > separate metadata file was good because it allowed a fast check of "does
>> > this distribution expose entry points?" Note that this isn't a useful
> thing
>> > to check for script wrappers, which again argues that those should be
>> > handled separately.
>
> That seems generally true, except that there might be applications out there
> that want to walk over the scripts associated with different installed
> distributions. That seems a legitimate, though uncommon, use case.
>
> In any case, I think the script metadata should be structured as
>
> "scripts": {
>   "console": [spec1, spec2]
>   "gui": [spec1, spec2]
> }
>
> Because that allows a sensible place for e.g. script generation options, as
> in
>
> "scripts": {
>   "console": [spec1, spec2]
>   "gui": [spec1, spec2]
>   "options": { ... }
> }
>
>
>> I am more interested in seeing the installer update some kind of index
>> like a sqlite database. I don't know if it would be faster since I
>> haven't tried it.
>
> That (a SQLite installation database) is probably some way off, and would
> require more significant changes elsewhere. The big advantage of the current
> setup with text files is that every thing is human readable - very handy
> when
> things go wrong. I don't know whether this area is a performance bottleneck,
> but we will be able to deal with it using a separate exports.json file in
> the
> short term.

Who knows. On some filesystems stat() is painfully slow and you could
be better off just parsing the single metadata file.

>> For one thing you can have more than one mysql = in the same
>> sqlalchemy.dialects. I think in this instance the string parsing is
>
> Don't you say in the PEP about the key that "It must be locally unique
> within
> this distribution’s group."?

The kind of entry point has to be unique, but the name inside the spec does not:

dialects : [
"mysql = first mysql driver...",
"mysql = second mysql driver..."
]

>> probably simpler than defining a more JSONy version.
>
> I think Paul's point is that if it was JSON, you wouldn't need to parse
> anything. The current format of entries is
>
> name = module:attrs [flag1,flag2]
>
> which could be { "name": name, "module": module, "attrs": attrs, "flags":
> ["flag1", "flag2"] } which is obviously more verbose.
>
> Note that I don't see necessarily a connection between extras and flags,
> though
> you've mentioned that they're extras. Does setuptools store, against an
> installed distribution, the extras it was installed with? AFAIK it doesn't.
> (Even if it did, it would need to keep that updated if one of the extras'
> dependencies were later uninstalled.) And if not, how would having extras in
> the specification help, since  you can't test the "must be installed" part?
> On
> the other hand, you might want to use generalised flags that provide control
> over how the exported entry is processed.

You might mean the document's mention that in setuptools loading an
entry point can require a particular extra. In setuptools this would
mean additional eggs could be added to sys.path as a result of loading
the entry point.

> One reason for keeping the format as-is might be in case any migration
> issues
> come up (i.e. people depending on this specific format in some way), but I'm
> not sure whether there are any such issues or what they might be.
>
>> FWIW the PEP 426 metadata is also full of structured strings.
>
> True - the dependency specifier, if nothing else.
>
> One other thing is that the PEP needs to state that the exports metadata
> must
> be written to exports.json in the .dist-info folder by an installer - that
> isn't mentioned anywhere. Also, whether it should contain the scripts part,
> or
> just the other exports (but see my comment above as to why scripts might be
> considered exports worth iterating over, like any other).

I would like to see it timed with and without exports.json

Why not keep a single API for iterating over console scripts and other
entry points and exports. Seems harmless.

> Regards,
>
> Vinay Sajip
>
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