Lib/anydbm.py

   1 """Generic interface to all dbm clones.
   2
   3 Instead of
   4
   5         import dbm
   6         d = dbm.open(file, 'w', 0666)
   7
   8 use
   9
  10         import anydbm
  11         d = anydbm.open(file, 'w')
  12
  13 The returned object is a dbhash, gdbm, dbm or dumbdbm object,
  14 dependent on the type of database being opened (determined by whichdb
  15 module) in the case of an existing dbm. If the dbm does not exist and
  16 the create or new flag ('c' or 'n') was specified, the dbm type will
  17 be determined by the availability of the modules (tested in the above
  18 order).
  19
  20 It has the following interface (key and data are strings):
  21
  22         d[key] = data   # store data at key (may override data at
  23                         # existing key)
  24         data = d[key]   # retrieve data at key (raise KeyError if no
  25                         # such key)
  26         del d[key]      # delete data stored at key (raises KeyError
  27                         # if no such key)
  28         flag = key in d   # true if the key exists
  29         list = d.keys() # return a list of all existing keys (slow!)
  30
  31 Future versions may change the order in which implementations are
  32 tested for existence, add interfaces to other dbm-like
  33 implementations.
  34
  35 The open function has an optional second argument.  This can be 'r',
  36 for read-only access, 'w', for read-write access of an existing
  37 database, 'c' for read-write access to a new or existing database, and
  38 'n' for read-write access to a new database.  The default is 'r'.
  39
  40 Note: 'r' and 'w' fail if the database doesn't exist; 'c' creates it
  41 only if it doesn't exist; and 'n' always creates a new database.
  42
  43 """
  44
  45 class error(Exception):
  46     pass
  47
  48 _names = ['dbhash', 'gdbm', 'dbm', 'dumbdbm']
  49 _errors = [error]
  50 _defaultmod = None
  51
  52 for _name in _names:
  53     try:
  54         _mod = __import__(_name)
  55     except ImportError:
  56         continue
  57     if not _defaultmod:
  58         _defaultmod = _mod
  59     _errors.append(_mod.error)
  60
  61 if not _defaultmod:
  62     raise ImportError, "no dbm clone found; tried %s" % _names
  63
  64 error = tuple(_errors)
  65
  66 def open(file, flag = 'r', mode = 0666):
  67     # guess the type of an existing database
  68     from whichdb import whichdb
  69     result=whichdb(file)
  70     if result is None:
  71         # db doesn't exist
  72         if 'c' in flag or 'n' in flag:
  73             # file doesn't exist and the new
  74             # flag was used so use default type
  75             mod = _defaultmod
  76         else:
  77             raise error, "need 'c' or 'n' flag to open new db"
  78     elif result == "":
  79         # db type cannot be determined
  80         raise error, "db type could not be determined"
  81     else:
  82         mod = __import__(result)
  83     return mod.open(file, flag, mode)