Allow make_dsn to take no parameter

The behaviour of connect() is unchanged: either dsn or params must be
specified.

doc/src/extensions.rst

@@ -497,11 +497,8 @@ Other functions
 
     Put together the arguments in *kwargs* into a connection string. If *dsn*
     is specified too, merge the arguments coming from both the sources. If the
-    same argument is specified in both the sources, the *kwargs* version
-    overrides the *dsn* version.
-
-    At least one parameter is required (either *dsn* or any keyword). Note
-    that the empty string is a valid connection string.
+    same argument name is specified in both the sources, the *kwargs* value
+    overrides the *dsn* value.
 
     The input arguments are validated: the output should always be a valid
     connection string (as far as `parse_dsn()` is concerned). If not raise

lib/__init__.py

@@ -116,6 +116,9 @@ def connect(dsn=None, connection_factory=None, cursor_factory=None,
     library: the list of supported parameters depends on the library version.
 
     """
+    if dsn is None and not kwargs:
+        raise TypeError('missing dsn and no parameters')
+
     dsn = _ext.make_dsn(dsn, **kwargs)
     conn = _connect(dsn, connection_factory=connection_factory, async=async)
     if cursor_factory is not None:

lib/extensions.py

@@ -158,7 +158,7 @@ class NoneAdapter(object):
 def make_dsn(dsn=None, **kwargs):
     """Convert a set of keywords into a connection strings."""
     if dsn is None and not kwargs:
-        raise TypeError('missing dsn and no parameters')
+        return ''
 
     # If no kwarg is specified don't mung the dsn, but verify it
     if not kwargs:

tests/test_connection.py

@@ -381,8 +381,8 @@ class MakeDsnTestCase(ConnectingTestCase):
     def assertDsnEqual(self, dsn1, dsn2):
         self.assertEqual(set(dsn1.split()), set(dsn2.split()))
 
-    def test_there_has_to_be_something(self):
-        self.assertRaises(TypeError, ext.make_dsn)
+    def test_empty_arguments(self):
+        self.assertEqual(ext.make_dsn(), '')
 
     def test_empty_string(self):
         dsn = ext.make_dsn('')