Since GTK+ 3.0 and the broad introduction of GObject Introspection (GIR) one now can switch from using the existing GnomeKeyring Python module to direct GIR-based access. This allows reducing the Python runtime dependency. Below you find a simple keyring access script unlocking a keyring named "test" adding a new entry and dumping all entries in the keyring. This code uses the generic secret keyring type and was originally written for a Liferea plugin that allows Liferea to store feed passwords into GnomeKeyring: 
from gi.repository import GObject
from gi.repository import GnomeKeyring

keyringName = 'test'

def unlock():
	print 'Unlocking keyring %s...' % keyringName
	GnomeKeyring.unlock_sync(keyringName, None)

def dump_all():
	print "Dump all keyring entries..."
	(result, ids) = GnomeKeyring.list_item_ids_sync(keyringName)
	for id in ids:	
	   (result, item) = GnomeKeyring.item_get_info_sync(keyringName, id)
	   if result != GnomeKeyring.Result.OK:
	      print '%s is locked!' % (id)
	   else:
	         print '  => %s = %s' % (item.get_display_name(), item.get_secret())

def do_query(id):
	print 'Fetch secret for id %s' % id
	attrs = GnomeKeyring.Attribute.list_new()
	GnomeKeyring.Attribute.list_append_string(attrs, 'id', id)
	result, value = GnomeKeyring.find_items_sync(GnomeKeyring.ItemType.GENERIC_SECRET, attrs)
	if result != GnomeKeyring.Result.OK:
		return

        print '  => password %s = %s' % (id, value[0].secret)
	print '     keyring id  = %s' % value[0].item_id

def do_store(id, username, password):
	print 'Adding keyring entry for id %s' % id
	GnomeKeyring.create_sync(keyringName, None)
	attrs = GnomeKeyring.Attribute.list_new()
	GnomeKeyring.Attribute.list_append_string(attrs, 'id', id)
	GnomeKeyring.item_create_sync(keyringName, GnomeKeyring.ItemType.GENERIC_SECRET, repr(id), attrs, '@@@'.join([username, password]), True)
	print '  => Stored.'

# Our test code...
unlock()
dump_all()
do_store('id1', 'User1', 'Password1')
do_query('id1')
dump_all()
For simplicity the username and password are stored together as the secret token separated by "@@@". According to the documentation it should be possible to store them separately, but given my limited Python knowledge and the missing GIR documentation made me use this simple method. If I find a better way I'll update this post. If you know how to improve the code please post a comment! The code should raise a keyring password dialog when run for the first time in the session and give an output similar to this: 
Unlocking keyring test...
Dump all keyring entries...
  => 'id1' = [email protected]@@PassA
Adding keyring entry for id id1
  => Stored.
Fetch secret for id id1
  => password id1 = [email protected]@@PassA
     keyring id  = 1
Dump all keyring entries...
  => 'id1' = [email protected]@@PassA
You can also check the keyring contents using the seahorse GUI where you should see the "test" keyring with an entry with id "1" as in the screenshot below.