Yesterday evening I gave a lightning talk at the Python User Group Berlin called “Showing BVG Departures In Your Office“. You can download the slides here.
The whole idea to the project came up when our student organization (Freitagsrunde) had to relocate to a new building at the end of 2012.
Since our new student organization meeting room is quite near to the next bus stop (bee-line), but the actual distance is way longer and we have to cross several doors, waiting in the room and heading to the bus stop when the bus arrives is not going to work.
As computer scientists we had to come up with a solution to somehow grab the departures of the bus stop and show them in the room.
At first the information retrieval was hard-coded and it was only possible to get the departures for a single bus stop. After a short time we got the feature request to also display the departures of nearby subways and other public transport. We ended up rewriting the entire application and created a library we then called bvg-grabber.
The quite simple API allows us to use both information provided by the BVG: the actual departures which, in that days, only returned departures about busses, and the scheduled departures as they are written on the time tables:
A class inheriting from QueryApi must implement a call() function that returns a Response object.
class QueryApi(object):
"""Performs the requests to the data source"""
def call(self):
"""Needs to return a Response"""
raise NotImplementedError("The inheriting class needs to "
"implement the call() method!")
A Response object must contain a state (True/False for success/failed request) and, for a successful request, the departing station and a list of Departures, or, for a failed request, the error that occurred.
class Response(object):
"""Returned by a QueryApi, contains list of Departures"""
def __init__(self, state, station=None, departures=None,
error=None):
self._state = state
self._departures = [(station, departures)]
self._error = error
@property
def departures(self):
return self._departures
Finally, a Departure defines when a certain line leaves at a certain start station and at which station the ride will end.
@total_ordering
class Departure(object):
"""Start and end station, next departure time"""
def __init__(self, start, end, when, line, since=None,
no_add_day=False):
# Some magic happens here
As we are using the actual and the scheduled information from the BVG as you can see above, here are 2 short examples how to use them:
In [1]: from bvggrabber.api.actualdeparture import ActualDepartureQueryApi
In [2]: resp = ActualDepartureQueryApi("Ernst-Reuter-Platz").call()
In [3]: resp.departures
Out[3]:
[('Ernst-Reuter-Platz',
[Start: Ernst-Reuter-Platz, End: S+U Zoologischer Garten, when: 13:56, now: 13:54, line: Bus 245,
Start: Ernst-Reuter-Platz, End: S+U Zoologischer Garten, when: 14:01, now: 13:54, line: Bus X9,
Start: Ernst-Reuter-Platz, End: S+U Zoologischer Garten, when: 14:05, now: 13:54, line: Bus M45,
Start: Ernst-Reuter-Platz, End: Johannesstift, when: 13:54, now: 13:54, line: Bus M45,
Start: Ernst-Reuter-Platz, End: Flughafen Tegel, when: 13:55, now: 13:54, line: Bus X9,
Start: Ernst-Reuter-Platz, End: Johannesstift, when: 14:01, now: 13:54, line: Bus M45])]
In [4]: from bvggrabber.api.scheduleddeparture import ScheduledDepartureQueryApi
In [5]: resp = ScheduledDepartureQueryApi("Ernst-Reuter-Platz").call()
In [6]: resp.departures
Out[6]:
[('Ernst-Reuter-Platz',
[Start: Ernst-Reuter-Platz, End: Johannesstift (Berlin), when: 13:54, now: 13:54, line: Bus M45,
Start: Ernst-Reuter-Platz, End: Hertzallee (Berlin), when: 13:56, now: 13:54, line: Bus 245,
Start: Ernst-Reuter-Platz, End: S+U Pankow (Berlin), when: 13:56, now: 13:54, line: U2,
Start: Ernst-Reuter-Platz, End: Hertzallee (Berlin), when: 13:57, now: 13:54, line: Bus M45,
Start: Ernst-Reuter-Platz, End: U Theodor-Heuss-Platz (Berlin), when: 13:58, now: 13:54, line: U2])]
I’m looking forward to your ideas and feature requests.
Markus