added an example for mutable_instance usage

README.md

@@ -131,6 +131,49 @@ The core of the PyConstClasses package are the `const_class` and `static_const_c
     Error: Cannot modify const attribute `version` of class `ProjectConfiguration`
     ```
 
+    Although the `static_const_class` decorator prevents "standard" class instantiation, you can create mutable instances of such classes:
+
+    ```python
+    @cc.static_const_class
+    class DatabaseConfiguration:
+        host: str = "localhost"
+        port: int = 5432
+        username: str = "admin"
+        password: str = "secret"
+
+        def __repr__(self):
+            return (
+                f"DatabaseConfiguration:\n"
+                f"Host: {self.host}\n"
+                f"Port: {self.port}\n"
+                f"Username: {self.username}\n"
+                f"Password: {self.password}"
+            )
+
+
+    if __name__ == "__main__":
+        print(f"Database configuration:\n{DatabaseConfiguration}")
+
+        try:
+            DatabaseConfiguration.host = "remotehost"
+        except cc.ConstError as err:
+            print(f"Error: {err}")
+
+        try:
+            DatabaseConfiguration.port = 3306
+        except cc.ConstError as err:
+            print(f"Error: {err}")
+
+        # Create a mutable instance for testing or development
+        mutable_config = cc.mutable_instance(DatabaseConfiguration)
+        mutable_config.host = "testhost"
+        mutable_config.username = "testuser"
+        mutable_config.password = "testpassword"
+
+        print("\nMutable configuration for testing:")
+        print(mutable_config)
+    ```
+
 > [!IMPORTANT]
 > In the current version of the package the constant attributes have to be defined using annotations, i.e. the `member: type (= value)` syntax of the class member declaration is required
 

examples/static_const_class_mutable_instance.py

@@ -0,0 +1,41 @@
+import constclasses as cc
+
+
+@cc.static_const_class
+class DatabaseConfiguration:
+    host: str = "localhost"
+    port: int = 5432
+    username: str = "admin"
+    password: str = "secret"
+
+    def __repr__(self):
+        return (
+            f"DatabaseConfiguration:\n"
+            f"Host: {self.host}\n"
+            f"Port: {self.port}\n"
+            f"Username: {self.username}\n"
+            f"Password: {self.password}"
+        )
+
+
+if __name__ == "__main__":
+    print(f"Database configuration:\n{DatabaseConfiguration}")
+
+    try:
+        DatabaseConfiguration.host = "remotehost"
+    except cc.ConstError as err:
+        print(f"Error: {err}")
+
+    try:
+        DatabaseConfiguration.port = 3306
+    except cc.ConstError as err:
+        print(f"Error: {err}")
+
+    # Create a mutable instance for testing or development
+    mutable_config = cc.mutable_instance(DatabaseConfiguration)
+    mutable_config.host = "testhost"
+    mutable_config.username = "testuser"
+    mutable_config.password = "testpassword"
+
+    print("\nMutable configuration for testing:")
+    print(mutable_config)

test/test_static_const_class.py

@@ -36,22 +36,6 @@ def test_member_modification():
         assert util.msg(err) == util.const_error_msg(attr_name, STATIC_CONST_CLASS_NAME)
 
 
-def test_mutable_instance_of_static_const_class():
-    mut_instance = mutable_instance(StaticConstClass)
-
-    for attr_name in ATTR_NAMES:
-        assert getattr(mut_instance, attr_name) == ATTR_VALS_1[attr_name]
-        setattr(mut_instance, attr_name, ATTR_VALS_2[attr_name])
-        assert getattr(mut_instance, attr_name) == ATTR_VALS_2[attr_name]
-
-    for attr_name in MANDATORY_CONST_ATTRS:
-        with pytest.raises(ConstError) as err:
-            setattr(mut_instance, attr_name, DUMMY_VALUE)
-        assert util.msg(err) == util.const_error_msg(
-            "mutable_StaticConstClass", attr_name
-        )
-
-
 def test_member_modification_with_include_parameter():
     include = {X_ATTR_NAME}
 
@@ -136,3 +120,20 @@ class StaticConstClassStrictTypes:
         with pytest.raises(TypeError) as err:
             setattr(StaticConstClassStrictTypes, attr_name, DUMMY_VALUE)
         assert util.msg(err).startswith(util.invalid_type_error_msg_prefix())
+
+
+def test_mutable_instance_of_static_const_class():
+    mut_instance = mutable_instance(StaticConstClass)
+
+    for attr_name in ATTR_NAMES:
+        assert getattr(mut_instance, attr_name) == ATTR_VALS_1[attr_name]
+        setattr(mut_instance, attr_name, ATTR_VALS_2[attr_name])
+        assert getattr(mut_instance, attr_name) == ATTR_VALS_2[attr_name]
+
+    for attr_name in MANDATORY_CONST_ATTRS:
+        assert not getattr(mut_instance, attr_name)
+        with pytest.raises(ConstError) as err:
+            setattr(mut_instance, attr_name, DUMMY_VALUE)
+        assert util.msg(err) == util.const_error_msg(
+            "mutable_StaticConstClass", attr_name
+        )