1 files changed, 47 insertions, 14 deletions

diff --git a/Lib/anydbm.py b/Lib/anydbm.py
index 2dc312d..ef913bb 100644
--- a/Lib/anydbm.py
+++ b/Lib/anydbm.py
@@ -8,10 +8,14 @@ Instead of
 use
 
 	import anydbm
-	d = anydbm.open(file)
+	d = anydbm.open(file, 'w')
 
 The returned object is a dbhash, gdbm, dbm or dumbdbm object,
-dependent on availability of the modules (tested in this order).
+dependent on the type of database being opened (determined by whichdb
+module) in the case of an existing dbm. If the dbm does not exist and
+the create or new flag ('c' or 'n') was specified, the dbm type will
+be determined by the availability of the modules (tested in the above
+order).
 
 It has the following interface (key and data are strings):
 
@@ -26,29 +30,58 @@ It has the following interface (key and data are strings):
 
 Future versions may change the order in which implementations are
 tested for existence, add interfaces to other dbm-like
-implementations, and (in the presence of multiple implementations)
-decide which module to use based upon the extension or contents of an
-existing database file.
+implementations.
 
-The open function has an optional second argument.  This can be set to
-'r' to open the database for reading only.  The default is 'r', like
-the dbm default.
+The open function has an optional second argument.  This can be 'r',
+for read-only access, 'w', for read-write access of an existing
+database, 'n' or 'c' for read-write access to a new database.  The
+default is 'r'.
+
+Note: the difference between 'w' and 'n' is that 'w' fails if the
+database doesn't already exist.  There appears to be no difference
+between 'n' and 'c'.
 
 """
 
+try:
+	class error(Exception):
+		pass
+except:
+	error = "anydbm.error"
+
 _names = ['dbhash', 'gdbm', 'dbm', 'dumbdbm']
+_errors = [error]
+_defaultmod = None
 
 for _name in _names:
 	try:
-		exec "import %s; _mod = %s" % (_name, _name)
+		_mod = __import__(_name)
 	except ImportError:
 		continue
-	else:
-		break
-else:
+	if not _defaultmod:
+		_defaultmod = _mod
+	_errors.append(_mod.error)
+
+if not _defaultmod:
 	raise ImportError, "no dbm clone found; tried %s" % _names
 
-error = _mod.error
+error = tuple(_errors)
 
 def open(file, flag = 'r', mode = 0666):
-	return _mod.open(file, flag, mode)
+	# guess the type of an existing database
+	from whichdb import whichdb
+	result=whichdb(file)
+	if result is None:
+		# db doesn't exist
+		if 'c' in flag or 'n' in flag:
+			# file doesn't exist and the new
+			# flag was used so use default type
+			mod = _defaultmod
+		else:
+			raise error, "need 'c' or 'n' flag to open new db"
+	elif result == "":
+		# db type cannot be determined
+		raise error, "db type could not be determined"
+	else:
+		mod = __import__(result)
+	return mod.open(file, flag, mode)