Fix/make project config immutable

changelog.txt

@@ -35,6 +35,11 @@ Fixed
 
  - Attempting to create a linked view for a Project on Windows now raises an informative error message.
 
+Deprecated
+++++++++++
+
+ - In-memory modification of the project configuration, to be removed in 2.0 (#246).
+
 Removed
 +++++++
 

signac/contrib/project.py

@@ -24,7 +24,7 @@
 from ..core.jsondict import JSONDict
 from ..core.h5store import H5StoreManager
 from .collection import Collection
-from ..common.config import load_config
+from ..common.config import load_config, Config
 from ..sync import sync_projects
 from .job import Job
 from .hashing import calc_id
@@ -95,6 +95,25 @@ def find_job_ids(self, filter=None, doc_filter=None):
         return self._collection._find(filter)
 
 
+class _ProjectConfig(Config):
+    """Extends the project config to make it immutable."""
+    def __init__(self, *args, **kwargs):
+        self._mutable = True
+        super(_ProjectConfig, self).__init__(*args, **kwargs)
+        self._mutable = False
+
+    def __setitem__(self, key, value):
+        if not self._mutable:
+            warnings.warn("Modifying the project configuration after project "
+                          "initialization is deprecated as of version 1.3 and "
+                          "will be removed in version 2.0.",
+                          DeprecationWarning)
+
+            from packaging import version
+            assert version.parse(__version__) < version.parse("2.0")
+        return super(_ProjectConfig, self).__setitem__(key, value)
+
+
 class Project(object):
     """The handle on a signac project.
 
@@ -120,7 +139,7 @@ class Project(object):
     def __init__(self, config=None):
         if config is None:
             config = load_config()
-        self._config = config
+        self._config = _ProjectConfig(config)
 
         # Ensure that the project id is configured.
         self.get_id()

tests/test_project.py

@@ -74,6 +74,16 @@ def test_root_directory(self):
     def test_workspace_directory(self):
         self.assertEqual(self._tmp_wd, self.project.workspace())
 
+    def test_config_modification(self):
+        # In-memory modification of the project configuration is
+        # deprecated as of 1.3, and will be removed in version 2.0.
+        # This unit test should reflect that change beginning 2.0,
+        # and check that the project configuration is immutable.
+        with warnings.catch_warnings(record=True) as w:
+            self.project.config['foo'] = 'bar'
+            self.assertEqual(len(w), 1)
+            self.assertEqual(w[0].category, DeprecationWarning)
+
     def test_workspace_directory_with_env_variable(self):
         os.environ['SIGNAC_ENV_DIR_TEST'] = self._tmp_wd
         self.project.config['workspace_dir'] = '${SIGNAC_ENV_DIR_TEST}'