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)