Extension of Python set() which is able to synchronize sets of comparable objects
Project description
SyncSet is an extension of the standard Python set(). With SyncSet, you can do set operations on sets of objects that, in addition to the normal unique ID of set members, has a changekey attribute (a timestamp, autoincrement value, revision ID etc.). Via set operations and a custom diff() method, you can do one- or two-way synchronization of comparable object sets via the OneWaySyncSet and TwoWaySyncSet classes, respectively. Examples are syncing files, contacts and calendar items.
Usage
Let’s say you want so refresh a local copy of some URLs from a server. You get a timestamp from the Last-Modified HTTP header. I’m using date for sake of brevity.
First, we want to tell syncset what constitutes a unique ID is and what constitutes a revision (changekey). We subclass SyncSetMember and make url the unique ID and last_modified the changekey.
>>> import syncset >>> from datetime import date >>> >>> class SyncURL(syncset.SyncSetMember): >>> def __init__(self, url, last_modified): >>> self.url = url >>> self.last_modified = last_modified >>> >>> def get_id(self): return self.url >>> def get_changekey(self): return self.last_modified >>> def __repr__(self): return self.__class__.__name__+repr((self.url, self.last_modified))
We want to sync these URLs:
>>> foo = "http://mysrv/foo.html" >>> bar = "http://mysrv/bar.html" >>> baz = "http://mysrv/baz.html"
This is our outdated copy:
>>> myurls = syncset.OneWaySyncSet() >>> myurls.add(SyncURL(foo, date(2012, 1, 1))) >>> myurls.add(SyncURL(bar, date(2011, 12, 8)))
This is the server version. You could get the Last-Modified header in an HTTP HEAD request:
>>> serverurls = syncset.OneWaySyncSet() >>> serverurls.add(SyncURL(foo, date(2012, 2, 1))) >>> serverurls.add(SyncURL(bar, date(2011, 12, 8))) >>> serverurls.add(SyncURL(baz, date(2012, 2, 15)))
Now, show us the difference between the two. diff() returns four SyncSet (only_in_self, only_in_master, outdated_in_self, updated_in_master):
>>> only_in_self, only_in_master, outdated_in_self, updated_in_master = myurls.diff(serverurls)
>>> only_in_self
OneWaySyncSet([])
>>> only_in_master
OneWaySyncSet([SyncURL('http://mysrv/baz.html', datetime.date(2012, 2, 15))])
>>> outdated_in_self
neWaySyncSet([SyncURL('http://mysrv/foo.html', datetime.date(2012, 1, 1))])
>>> updated_in_master
OneWaySyncSet([SyncURL('http://mysrv/foo.html', datetime.date(2012, 2, 1))])
As you can see, foo needs to be updated, bar is unchanged and baz is new on the server. [Now we do whatever is needed to fetch the new and updated data in our program]. Let’s update the local copy:
>>> myurls.update(serverurls)
OneWaySyncSet([SyncURL('http://mysrv/foo.html', datetime.date(2012, 2, 1)), SyncURL('http://mysrv/bar.html', \
... datetime.date(2011, 12, 8)), SyncURL('http://mysrv/baz.html', datetime.date(2012, 2, 15))])
This updates foo and adds baz.
Similarly, a TwoWaySyncSet class exists that implements two-way synchronization. Boths versions implement all the normal set() operations, using either one-way or two-way sync semantics.
