If you are on Python 3.4+ you can use the functools.singledispatch decorator to do this (with a little extra help from the methoddispatch decorator that @ZeroPiraeus wrote for his answer):
class Container:
@methoddispatch
def __init__(self):
self.timestamp = 0
self.data = []
self.metadata = {}
@__init__.register(File)
def __init__(self, file):
f = file.open()
self.timestamp = f.get_timestamp()
self.data = f.get_data()
self.metadata = f.get_metadata()
@__init__.register(Timestamp)
def __init__(self, timestamp, data, metadata):
self.timestamp = timestamp
self.data = data
self.metadata = metadata
