DShare is a small Python utility that synchronizes contacts between two or more Gmail accounts.

Sharing is performed between designated contact groups.
The group name indicates which remote group/account to share with.

For instance, if User1 has a group named "Friends [User2]", that group will be kept synchronized with the "Friends"
group belonging to User2.

It is intended to be run periodically (i.e. as a cron job).

At the moment, it seems to work, but is missing a ton of features and polish. Contributors welcome!

===== Usage: =====

Add an account to the database:
  dshare.py -a <usertag>

This will generate a URL that will prompt you to grant this application read/write access to your gmail contacts.
When you visit this URL, make sure you're logged into gmail under the account you wish to add.
Note that <usertag> has no relation to your actual gmail username, unless you choose to make them the same.
Once access is granted, Google will return an authentication token.  This token is what's stored in the database;
never your password.

Remove an account from the database:
  dshare.py -d <usertag>

List all accounts in the database:
  dshare.py -l

Synchronize all accounts in the database:
  dshare.py -s

Test mode; pretend to synchronize but don't write any changes:
  dshare.py -t

Sharing is performed on a per-group basis.  Any group with a name of the form "Name [tag]" (a Slave group) will be
kept in sync with the corresponding Master group called "Name" belonging to the account with usertag "tag".  Any number
of Slaves can point to the same Master.  A Slave cannot be a Master (i.e., groups with names like "Name [tag1] [tag2]"
are rejected).

The Master/Slave concept does not imply a difference in permissions.  Any account can change any shared contact, and
the change will be propagated as needed.  At the moment there is no concept of access control or asymmetric
permissions. That means DShare is currently most useful for small groups of peers, such as a family wanting a shared
contact database (which was my motivation for creating it).

Within a shared contact group, additions, deletions, and modifications of contacts are propagated to all other mirrors
of the group.

If more than one account modifies a contact between synchronizations, DShare takes the conservative approach and splits
the contact into two coexisting versions.  Since both versions will be shared, all accounts will wind up with both
versions.  GMail's excellent contact merge tool can then be used to merge them together, resulting in the deletion of
one of the two versions.  (The merge and the deletion will be propagated at the next sync as usual).