invirt.common: give clearer error message on missing config variable

[invirt/packages/invirt-base.git] / python / invirt / common.py

diff --git a/python/invirt/common.py b/python/invirt/common.py
index 2cf860d..85f37d6 100644 (file)
--- a/python/invirt/common.py
+++ b/python/invirt/common.py
@@ -4,22 +4,41 @@ import unittest
 from fcntl import flock, LOCK_EX, LOCK_SH, LOCK_UN
 import contextlib as clib
 
+class InvirtConfigError(AttributeError):
+    pass
+
 class struct(object):
     'A simple namespace object.'
-    def __init__(self, d = {}, **kwargs):
-        'd is the dictionary to update my __dict__ with.'
+    def __init__(self, d = {}, __prefix = None, **kwargs):
+        'd is the dictionary or the items-iterable to update my __dict__ with.'
         self.__dict__.update(d)
         self.__dict__.update(kwargs)
+        self.__prefix = __prefix
+    def __getattr__(self, key):
+        # XX ideally these would point a frame higher on the stack.
+        prefix = self.__prefix
+        if prefix is not None:
+            raise InvirtConfigError('missing configuration variable %s%s'
+                                    % (prefix, key))
+        else:
+            raise AttributeError("anonymous struct has no member '%s'"
+                                 % (key,))
 
-def dicts2struct(x):
+def dicts2struct(x, prefix = None):
     """
     Given a tree of lists/dicts, perform a deep traversal to transform all the
     dicts to structs.
     """
+    if prefix is not None:
+        def newprefix(k): return prefix + str(k) + '.'
+    else:
+        def newprefix(k): return prefix
     if type(x) == dict:
-        return struct((k, dicts2struct(v)) for k,v in x.iteritems())
+        return struct(((k, dicts2struct(v, newprefix(k)))
+                       for k,v in x.iteritems()),
+                      prefix)
     elif type(x) == list:
-        return [dicts2struct(v) for v in x]
+        return [dicts2struct(v, newprefix(i)) for i, v in enumerate(x)]
     else:
         return x
 
@@ -67,7 +86,7 @@ class common_tests(unittest.TestCase):
                 'dict': { 'atom': 'atom', 'list': [1,2,3] },
                 'list': [ 'atom', {'key': 'value'} ]
                 }
-        structs = dicts2struct(dicts)
+        structs = dicts2struct(dicts, '')
         self.assertEqual(structs.atom,        dicts['atom'])
         self.assertEqual(structs.dict.atom,   dicts['dict']['atom'])
         self.assertEqual(structs.dict.list,   dicts['dict']['list'])