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Controlling the storage of data
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  ($Id$)
  >>> import os
  >>> from cybertools import storage
  >>> directory = os.path.dirname(storage.__file__)
  >>> from cybertools.storage.filesystem import explicitDirectoryStorage
  >>> storage = explicitDirectoryStorage(os.path.join(directory, 'testdata'))
  >>> storage.getDir('demo')
  '/home/.../cybertools/storage/testdata/demo'
  >>> from cybertools.storage.filesystem import instanceVarSubdirectoryStorage
  >>> storage = instanceVarSubdirectoryStorage()
  >>> storage.getDir('demo')
  '.../var/extfiles/demo'