[Python-Dev] PEP 426 comment: field order (original) (raw)

Daniel Holth dholth at gmail.com
Fri Oct 19 03:23:37 CEST 2012

Added some notes about the (lack of) ordering.

The email module provides an ordered multidict interface to the data. The first tag wins (if you improperly define Name: twice for example), but the order of everything is preserved. We just don't need it, except that it might be surprising to see your classifiers randomly re-ordered.

It is also possible to textwrap.dedent(p['Description']) with p = email.parser.Parser().parsestr(metadata).

I don't really expect anyone to use email.parser.Parser() so I'm hesitant to mention it, but it seems to work. I say it's read-only because the 3.2 Parser()/Generator() can't reserialize it due to Unicode. The improved Python 3.3 email module would be able to under the right conditions.

diff -r 79e95f487a33 -r 4773b6b3e8f2 pep-0426.txt --- a/pep-0426.txt Thu Oct 18 08:31:44 2012 +0100 +++ b/pep-0426.txt Thu Oct 18 21:10:26 2012 -0400 @@ -33,10 +33,14 @@

The syntax defined in this PEP is for use with Python distribution metadata files. The file format is a simple UTF-8 encoded Key: value -format with no maximum line length. It is parsable by the email +format with no maximum line length. It is parseable by the email module with an appropriate email.policy.Policy(). The field names listed in the Fields_ section are used as the header names.

+In Python 3.2, a serviceable read-only parser is:: +

@@ -66,7 +70,8 @@ times in a single metadata file. Other fields may only occur once in a metadata file. Fields marked with "(optional)" are not required to appear in a valid metadata file; all other -fields must be present. +fields must be present. The fields may appear in any order within +the file.

Metadata-Version :::::::::::::::: @@ -480,12 +485,17 @@

An ASCII string, not containing whitespace or the / character, that indicates the presence of extended metadata. Additional tags defined by -the extension should be of the form string/Name:: +an Extension: Chili should be of the form Chili/Name::

 Extension: Chili
 Chili/Type: Poblano
 Chili/Heat: Mild

+An implementation might iterate over all the declared Extension: +fields to invoke the processors for those extensions. As the order of +the fields is not used, the Extension: Chili field may appear before +or after its declared tags Chili/Type: etc. +

More information about the Python-Dev mailing list