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[roundup.git] / roundup / backends / __init__.py

diff --git a/roundup/backends/__init__.py b/roundup/backends/__init__.py
index 0b7ddebd73b23e75d61ba821b9dc6c7953b56224..1fc794888400e87c30a1df4ad50dd61ac872ef0e 100644 (file)
--- a/roundup/backends/__init__.py
+++ b/roundup/backends/__init__.py
@@ -14,29 +14,75 @@
 # FOR A PARTICULAR PURPOSE.  THE CODE PROVIDED HEREUNDER IS ON AN "AS IS"
 # BASIS, AND THERE IS NO OBLIGATION WHATSOEVER TO PROVIDE MAINTENANCE,
 # SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
-# 
-# $Id: __init__.py,v 1.27 2004-04-05 23:43:03 richard Exp $
+#
+# $Id: __init__.py,v 1.40 2007-11-07 20:47:12 richard Exp $
 
 '''Container for the hyperdb storage backend implementations.
-
-The __all__ variable is constructed containing only the backends which are
-available.
 '''
 __docformat__ = 'restructuredtext'
 
-__all__ = []
+import sys
 
-for backend in ['anydbm', ('mysql', 'MySQLdb'), ('bsddb', '_bsddb'),
-        'bsddb3', 'sqlite', 'metakit', ('postgresql', 'psycopg')]:
-    if len(backend) == 2:
-        backend, backend_module = backend
+# These names are used to suppress import errors.
+# If get_backend raises an ImportError with appropriate
+# module name, have_backend quietly returns False.
+# Otherwise the error is reraised.
+_modules = {
+    'mysql': ('MySQLdb',),
+    'postgresql': ('psycopg',),
+    'tsearch2': ('psycopg',),
+    'sqlite': ('pysqlite', 'pysqlite2', 'sqlite3', '_sqlite3', 'sqlite'),
+}
+
+def get_backend(name):
+    '''Get a specific backend by name.'''
+    vars = globals()
+    # if requested backend has been imported yet, return current instance
+    if name in vars:
+        return vars[name]
+    # import the backend module
+    module_name = 'back_%s' % name
+    try:
+        module = __import__(module_name, vars)
+    except:
+        # import failed, but in versions prior to 2.4, a (broken)
+        # module is left in sys.modules and package globals;
+        # subsequent imports would succeed and get the broken module.
+        # This no longer happens in Python 2.4 and later.
+        if sys.version_info < (2, 4):
+            del sys.modules['.'.join((__name__, module_name))]
+            del vars[module_name]
+        raise
     else:
-        backend_module = backend
+        vars[name] = module
+        return module
+
+def have_backend(name):
+    '''Is backend "name" available?'''
+    if name == 'tsearch2':
+        # currently not working
+        return 0
     try:
-        globals()[backend] = __import__('back_%s'%backend, globals())
-        __all__.append(backend)
+        get_backend(name)
+        return 1
     except ImportError, e:
-        if not str(e).startswith('No module named %s'%backend_module):
-            raise
+        for name in _modules.get(name, (name,)):
+            if str(e).startswith('No module named %s'%name):
+                return 0
+        raise
+    return 0
+
+def list_backends():
+    '''List all available backend names.
+
+    This function has side-effect of registering backward-compatible
+    globals for all available backends.
+
+    '''
+    l = []
+    for name in 'anydbm', 'mysql', 'sqlite', 'postgresql':
+        if have_backend(name):
+            l.append(name)
+    return l
 
-# vim: set filetype=python ts=4 sw=4 et si
+# vim: set filetype=python sts=4 sw=4 et si :