dbm.open(file, flag='r', mode=0o666)
Open the database file file and return a corresponding object.
If the database file already exists, the whichdb() function is used to determine its type and the appropriate module is used; if it does not exist, the first module listed above that can be imported is used.
The optional flag argument can be:
Value Meaning 'r' Open existing database for reading only (default) 'w' Open existing database for reading and writing 'c' Open database for reading and