[Python-checkins] peps: PEP 426: clarify metadata version transitions

[nick.coghlan]

http://hg.python.org/peps/rev/630c5dd5a123
changeset:   4751:630c5dd5a123
user:        Nick Coghlan <ncoghlan at gmail.com>
date:        Mon Feb 18 22:02:45 2013 +1000
summary:
  PEP 426: clarify metadata version transitions

files:
  pep-0426.txt |  28 ++++++++++++++++++++++------
  1 files changed, 22 insertions(+), 6 deletions(-)


diff --git a/pep-0426.txt b/pep-0426.txt
--- a/pep-0426.txt
+++ b/pep-0426.txt
@@ -89,9 +89,15 @@
 
 Version of the file format; "2.0" is the only legal value.
 
-Automated tools should warn if ``Metadata-Version`` is greater than the
-highest version they support, and must fail if ``Metadata-Version`` has
-a greater major version than the highest version they support.
+Automated tools consuming metadata should warn if ``Metadata-Version`` is
+greater than the highest version they support, and must fail if
+``Metadata-Version`` has a greater major version than the highest
+version they support.
+
+For broader compatibility, automated tools may choose to produce
+distribution metadata using the lowest metadata version that includes
+all of the needed fields.
+
 
 Example::
 
@@ -1283,9 +1289,19 @@
 metadata specifications is unlikely to give the expected behaviour.
 
 Whenever the major version number of the specification is incremented, it
-is expected that deployment will take some time, as metadata consuming tools
-much be updated before other tools can safely start producing the new
-format.
+is expected that deployment will take some time, as either metadata
+consuming tools must be updated before other tools can safely start
+producing the new format, or else the sdist and wheel formats, along with
+the installation database definition, will need to be updated to support
+provision of multiple versions of the metadata in parallel.
+
+Existing tools won't abide by this guideline until they're updated to
+support the new metadata standard, so the new semantics will first take
+effect for a hypothetical 2.x -> 3.0 transition. For the 1.x -> 2.0
+transition, it is recommended that tools continue to produce the
+existing supplementary files (such as ``entry_points.txt``) in addition
+to any equivalents specified using the new features of the standard
+metadata format (including the formal extension mechanism).
 
 
 Standard encoding and other format clarifications

-- 
Repository URL: http://hg.python.org/peps