[Python-Dev] Distutils ML wrap-up: setup.cfg new format (original) (raw)

Guido van Rossum guido at python.org
Wed Sep 23 04:28:41 CEST 2009

David,

Isn't it clear from Tarek's email that he is summarizing distutils-sig? Isn't it odd that you ask this question pointing to your own message? Are you worried that you won't get credit for the idea (assuming it's yours)? Should you perhaps just ask for credit instead of asking a rhetorical question?

--Guido

On Tue, Sep 22, 2009 at 5:07 PM, David Lyon <david.lyon at preisshare.net> wrote:

Tarek, Are you claiming this as your own work and ideas? Given: http://mail.python.org/pipermail/distutils-sig/2009-August/012998.html Regards David

On Tue, 22 Sep 2009 15:21:06 +0200, Tarek Ziadé <ziade.tarek at gmail.com> wrote: Hello

Here's a wrapup of the Distutils-SIG discussion we had on the "static metadata" topic. I realize that it's a good thing to send in. python-dev such wrapup on distutils design decisions, to keep everyone informed and get more feedback when required. I will try to do it for every upcoming changes that are not going in a PEP process (when it's not a 'big' change). The rate of such mails should not be very high. (around 1 mail in python-dev for +150 mails in distutils-SIG) If you feel that what we are about to change in distutils is wrong, you can go ahead and help us by participating in Distutils-ML, so we keep one and only one media for these discussions. The four sentences summary for people in a hurry: Getting metadata of a distribution that is not. installed means running its setup.py. This means. downloading the whole archive, and running. third party code on your system. To avoid it, we are adding a [setup] section in. setup.cfg where you can express the package metadata statically. Conditional sections, specific to some system. can be added to add some specific fields in [setup]. At the end, you will be able to get metadata fields without running any third-party code, and possibly get only the distribution setup.cfg for this. Now the long version.

Rational ======== Today, if you want to list all the metadata (PEP 314) of a. distribution that is not installed, you need to use it's. setup.py CLI. So, basically, you download it, and run:: $ python setup.py --name Foo $ python setup.py --version 1.2 Where name and version are metadata fields. That's OK but as. soon as the developers add more code in setup.py, this feature might break or (worse) might do unwanted things on the target. system. Why should we run third-party code just to get its metadata ? So we worked on a way to express those metadata statically, by pushing them in setup.cfg. That's not hard, since all. the metadata fields are static values. Adding a setup section in setup.cfg =================================== So the first thing we want to introduce is a [setup] section, that may contain any field from the metadata:: [setup] name: Foo version: 1.2 Distutils will look for them, and will use them. Of course setup.py is still required, and in case an option that is. a metadata field is passed to setup(), it will override one. located in setup.cfg. PEP 341 is coming up ==================== Remember the last Pycon Summit ? We said that we would introduce a new metadata field to describe requirements.. That's basically what PEP 341 is about, and we are still. working on it. Basically, we will be able to write things like:: requires: Twisted == 8.2.0 What takes us so long is that adding requirements like this in the metadata requires more things: - the ability to compare versions (this was described in. PEP 386 but not finished yet) - the ability to make these requirements vary depending on. the target system And the later makes our "setup.cfg" new [setup] section. obsolete as soon as this new metadata field is added in. Python. So we need more that what I've shown in the previous section Context-dependant sections ========================== The second change we are going to introduce is context-dependant sections in setup.cfg. A context dependant section is a section with a condition that is. used only if the execution environment meets its condition. Here's an example:: [setup] name: Foo version: 1.3 [setup:sysplatform == 'win32'] requires: pywin32 requires: bar > 1.0 [setup:osmachine == '64bits'] requires: somepackage [setup:pythonversion == '2.4' or pythonversion == '2.5'] requires: somepackage Every [setup:condition] section will be added in [setup] only if the condition is met. The micro-language behind this is the simplest possible: it compares only strings, with usual string operators, and with the ability to combine expressions. It makes it also easy to understand to non-pythoneers (os packagers). The pseudo-grammar is (I don't know how to write those but you'll get it hopefully):: comp: '<'|'>'|'=='|'>='|'<='|'<>'|'!='|'in'|'not' 'in' comparison: expr (compop expr)* expr: STRING test: ortest ortest: andtest ('or' andtest)* andtest: nottest ('and' nottest)* nottest: 'not' nottest | comparison where STRING belongs to any of those: - pythonversion = '%s.%s' % (sys.versioninfo[0], sys.versioninfo[1]) - osname = os.name - sysplatform = sys.platform - ossysname = os.uname()[0]. - osnodename = os.uname()[1] - osrelease = os.uname()[2]. - osversion = os.uname()[3].. - osmachine = os.uname()[4]. - a free string, like '2.4', or 'win32' Distutils will provide a function that is able to read the metadata of a distribution, given a setup.cfg file, for the target environment:: >>> from distutils.util import localmetadata >>> localmetadata('setup.cfg') Meaning that a Vanilla Python will be able to read the metadata of a package without running any code. That's what distutils will use when setup.py is run. That's what any package manager will be able to use to work. with distributions. Limitations =========== If a distribution is unable for obscure reasons (or does not wish) to set all metadata fields in setup.cfg, that's fine :. the fields will be set to UNKNOWN when localmetadata is called. When setup.py is run, options passed to setup() will complete those. When a package manager gets 'UNKOWN' values, it knows it might need to do further processing by running setup.py. Why this change is good ===================== Once the requires metadata is added in PEP 341, being able to query the metadata for a distribution can be done without doing anything else than reading a static file and interpreting its conditions in a restricted and secured manner. So there's no need to run third-party code anymore. Possible use cases: - setup.cfg is published on PyPI. Packages managers like easyinstall or pip will be able to list all the distributions needed and their versions for installing a distribution without having to download anything ! - OS packagers will be able to list the dependencies of a distribution without having to browse Python code. And, again, this new [setup] section is backward-compatible, and will be a good complement to the work done in PEP 376. Thanks for reading so far. This code will be added in 2.7 and 3.2. Tarek

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-- --Guido van Rossum (home page: http://www.python.org/~guido/)

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