chore(ruff): var name changes; unused import; formatting

Handle vars variable hiding builting vars().

Use more descripting variable name.

Remove unused sys import.

Add double lines where needed.

roundup/backends/__init__.py

@@ -19,8 +19,6 @@
 '''
 __docformat__ = 'restructuredtext'
 
-import sys
-
 # These names are used to suppress import errors.
 # If get_backend raises an ImportError with appropriate
 # module name, have_backend quietly returns False.
@@ -31,18 +29,20 @@
     'sqlite': ('sqlite3', '_sqlite3'),
 }
 
+
 def get_backend(name):
     '''Get a specific backend by name.'''
-    vars = globals()
+    global_vars = globals()
     # if requested backend has been imported yet, return current instance
-    if name in vars:
-        return vars[name]
+    if name in global_vars:
+        return global_vars[name]
     # import the backend module
     module_name = 'back_%s' % name
-    module = __import__(module_name, vars, level=1)
-    vars[name] = module
+    module = __import__(module_name, global_vars, level=1)
+    global_vars[name] = module
     return module
 
+
 def have_backend(name):
     '''Is backend "name" available?'''
     try:
@@ -62,6 +62,7 @@ def have_backend(name):
         raise
     return 0
 
+
 def list_backends():
     '''List all available backend names.
 
@@ -75,10 +76,10 @@ def list_backends():
     because we do not need to monkey-patch list_backends.
 
     '''
-    l = []
+    backend_list = []
     for name in 'anydbm', 'mysql', 'sqlite', 'postgresql', 'memorydb':
         if have_backend(name):
-            l.append(name)
-    return l
+            backend_list.append(name)
+    return backend_list
 
 # vim: set filetype=python sts=4 sw=4 et si :