Add backwards-compatibility for dot-based sectioning.

tests/test_config.py

@@ -28,6 +28,33 @@ def test_api_deprecation_warning():
             pass
 
 
+def test_api_redirect():
+    root = configdefaults.config
+    # one section level
+    root.add(
+        "test__section_redirect",
+        "A config var from a test case.",
+        configparser.StrParam("test_default"),
+    )
+    assert hasattr(root, "test__section_redirect")
+    assert root.test__section_redirect == "test_default"
+    assert hasattr(root, "test")
+    assert isinstance(root.test, configparser._SectionRedirect)
+    with pytest.warns(DeprecationWarning):
+        assert root.test.section_redirect == "test_default"
+
+    # two section levels
+    root.add(
+        "test__subsection__redirect",
+        "A config var from a test case.",
+        configparser.StrParam("test_default2"),
+    )
+    assert hasattr(root, "test__subsection__redirect")
+    assert root.test__subsection__redirect == "test_default2"
+    with pytest.warns(DeprecationWarning):
+        assert root.test.subsection.redirect == "test_default2"
+
+
 def test_invalid_default():
     # Ensure an invalid default value found in the Theano code only causes
     # a crash if it is not overridden by the user.

theano/configparser.py

@@ -74,6 +74,27 @@ def _hash_from_code(msg):
     return "m" + hashlib.sha256(msg).hexdigest()
 
 
+class _SectionRedirect:
+    """Functions as a mock property on the TheanoConfigParser.
+
+    It redirects attribute access (to config subsectinos) to the
+    new config variable properties that use "__" in their name.
+    """
+
+    def __init__(self, root, section_name):
+        self._root = root
+        self._section_name = section_name
+        super().__init__()
+
+    def __getattr__(self, attr):
+        warnings.warn(
+            f"Accessing section '{attr}' through old .-based API. "
+            f"This will be removed. Use 'config.{self._section_name}__{attr}' instead.",
+            DeprecationWarning,
+        )
+        return getattr(self._root, f"{self._section_name}__{attr}")
+
+
 class TheanoConfigParser:
     """ Object that holds configuration settings. """
 
@@ -175,6 +196,18 @@ class TheanoConfigParser:
         # keep the ConfigParam object in a dictionary:
         self._config_var_dict[name] = configparam
 
+        # The old API used dots for accessing a hierarchy of sections.
+        # The following code adds redirects that spill DeprecationWarnings
+        # while allowing backwards-compatible access to dot-based subsections.
+        # Because the subsectioning is recursive, redirects must be added for
+        # all levels. For example: ".test", ".test.subsection".
+        sections = name.split("__")
+        for s in range(1, len(sections)):
+            section_name = "__".join(sections[:s])
+            if not hasattr(self, section_name):
+                redirect = _SectionRedirect(self, section_name)
+                setattr(self.__class__, section_name, redirect)
+
     def fetch_val_for_key(self, key, delete_key=False):
         """Return the overriding config value for a key.
         A successful search returns a string value.