A exmaple with multiple VCALENDAR components::

  >>> from icalendar import Calendar
  >>> import os
  >>> directory = os.path.dirname(__file__)
  >>> cals = Calendar.from_string(
  ...   open(os.path.join(directory, 'multiple.ics'),'rb').read(), multiple=True)

  >>> for cal in cals:
  ...   for component in cal.walk():
  ...     component.name
  'VCALENDAR'
  'VEVENT'
  'VCALENDAR'
  'VEVENT'
  'VEVENT'

  >>> cals[0]['prodid']
  vText(u'-//Mozilla.org/NONSGML Mozilla Calendar V1.0//EN')

