Message Representations with __slots__

We have three classes for representing translatable messages and their translations on import/export:

• TranslationMessageData

• VPOExport

• VPOTExport

These are close to C struct types: just dumb collections of data, without ORM backing. The VPOExport and VPOTExport ones are old and redundant; we should be using TranslationMessageData instead.

To figure out what's really in these classes, I tried adding __slots__ to them and running the test suite. The branch is lp:~jtv/launchpad/slots.

TranslationMessageData contains:

• context
• msgid_singular
• msgid_plural
• singular_text
• plural_text
• _translations
• comment
• source_comment
• file_references
• file_references_list
• flags
• sequence
• nplurals
• is_obsolete

VPOExport contains:

• languagepack (may not be needed nowadays since we export one POFile at a time)

• potemplate (may not be needed nowadays since we export one POFile at a time)

• pofile (may not be needed nowadays since we export one POFile at a time)

• potmsgset_id
• potmsgset
• sequence
• context

• msgid_singular (needs explicit initialization to None if not present)

• msgid_plural (needs explicit initialization to None if not present)

• comment
• source_comment
• file_references
• flags_comment

• is_current (the recife work renames this to is_current_ubuntu)

• is_imported (the recife work renames this to is_current_upstream)

• diverged

• ['translation%d' for form in range TranslationConstants.MAX_PLURAL_FORMS]

VPOTExport contains:

• potemplate (may not be needed nowadays since we export one POFile at a time)

• potmsgset
• sequence
• context
• msgid_singular
• msgid_plural
• comment
• source_comment
• file_references
• flags_comment
• template_header

On a sidenote, adding __slots__ may improve import/export performance a bit by avoiding Python's massive object-creation overhead, and this proves that it can be done.