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      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, and add interfaces to other dbm-like
     33 implementations.
     34 """
     35 
     36 class error(Exception):
     37     pass
     38 
     39 _names = ['dbhash', 'gdbm', 'dbm', 'dumbdbm']
     40 _errors = [error]
     41 _defaultmod = None
     42 
     43 for _name in _names:
     44     try:
     45         _mod = __import__(_name)
     46     except ImportError:
     47         continue
     48     if not _defaultmod:
     49         _defaultmod = _mod
     50     _errors.append(_mod.error)
     51 
     52 if not _defaultmod:
     53     raise ImportError, "no dbm clone found; tried %s" % _names
     54 
     55 error = tuple(_errors)
     56 
     57 def open(file, flag='r', mode=0666):
     58     """Open or create database at path given by *file*.
     59 
     60     Optional argument *flag* can be 'r' (default) for read-only access, 'w'
     61     for read-write access of an existing database, 'c' for read-write access
     62     to a new or existing database, and 'n' for read-write access to a new
     63     database.
     64 
     65     Note: 'r' and 'w' fail if the database doesn't exist; 'c' creates it
     66     only if it doesn't exist; and 'n' always creates a new database.
     67     """
     68 
     69     # guess the type of an existing database
     70     from whichdb import whichdb
     71     result=whichdb(file)
     72     if result is None:
     73         # db doesn't exist
     74         if 'c' in flag or 'n' in flag:
     75             # file doesn't exist and the new
     76             # flag was used so use default type
     77             mod = _defaultmod
     78         else:
     79             raise error, "need 'c' or 'n' flag to open new db"
     80     elif result == "":
     81         # db type cannot be determined
     82         raise error, "db type could not be determined"
     83     else:
     84         mod = __import__(result)
     85     return mod.open(file, flag, mode)
     86