twisted.persisted.dirdbm.DirDBM is a DBM-like storage system. That is, it stores mappings between keys and values, like a Python dictionary, except that it stores the values in files in a directory - each entry is a different file. The keys must always be strings, as are the values. Other than that, DirDBM objects act just like Python dictionaries.
DirDBM is useful for cases when you want to store small amounts of data in an organized fashion, without having to deal with the complexity of a RDBMS or other sophisticated database. It is simple, easy to use, cross-platform, and doesn’t require any external C libraries, unlike Python’s built-in DBM modules.
>>> from twisted.persisted import dirdbm
>>> d = dirdbm.DirDBM("/tmp/dir")
>>> d["librarian"] = "ook"
>>> d["librarian"]
'ook'
>>> d.keys()
['librarian']
>>> del d["librarian"]
>>> d.items()
[]
Sometimes it is necessary to persist more complicated objects than strings.
With some care, dirdbm.Shelf
can transparently persist
them. Shelf works exactly like DirDBM , except that
the values (but not the keys) can be arbitrary picklable objects. However,
notice that mutating an object after it has been stored in the Shelf has no effect on the Shelf.
When mutating objects, it is necessary to explicitly store them back in the Shelf
afterwards:
>>> from twisted.persisted import dirdbm
>>> d = dirdbm.Shelf("/tmp/dir2")
>>> d["key"] = [1, 2]
>>> d["key"]
[1, 2]
>>> l = d["key"]
>>> l.append(3)
>>> d["key"]
[1, 2]
>>> d["key"] = l
>>> d["key"]
[1, 2, 3]