Implement class method Context::module_set_id.

examples/test/yang-library-data.json

 {
   "ietf-yang-library:modules-state": {
-    "module-set-id": "TO-BE-INVENTED",
+    "module-set-id": "b6d7e0614440c5ad8a7370fe46c777254d331983",
     "module": [
       {
         "name": "testb",

setup.py

@@ -10,7 +10,7 @@ def contents(*filenames):
 setup(
     name = "yangson",
     packages = ["yangson"],
-    version = "0.1.50",
+    version = "0.1.51",
     description = "Library for working with YANG schemas and data",
     author = "Ladislav Lhotka",
     author_email = "lhotka@nic.cz",

tests/test_model.py

@@ -122,6 +122,7 @@ def instance(data_model):
 
 def test_context(data_model):
     assert len(Context.implement) == 3
+    assert Context.module_set_id() == "b6d7e0614440c5ad8a7370fe46c777254d331983"
     tid = Context._last_revision("test")
     stid = Context._last_revision("subtest")
     tbid = Context._last_revision("testb")

yangson/context.py

+import hashlib
 import re
 from typing import Dict, List, MutableSet
 from .constants import pname_re, YangsonException
@@ -94,6 +95,13 @@ class Context:
         cls.schema._post_process()
         cls.schema._make_schema_patterns()
 
+    @classmethod
+    def module_set_id(cls):
+        """Return numeric id of the current set of modules."""
+        fnames = ["@".join(m) for m in cls.modules.keys()]
+        fnames.sort()
+        return hashlib.sha1("".join(fnames).encode("ascii")).hexdigest()
+
     @classmethod
     def _load_module(cls, name: YangIdentifier,
                     rev: RevisionDate) -> Statement: