[PYTHON] Enable environment scoping (#33)

vta/python/vta/environment.py

@@ -143,6 +143,15 @@ class Environment(object):
         self.mock_mode = False
         self._mock_env = None
         self._dev_ctx = None
+        self._last_env = None
+
+    def __enter__(self):
+        self._last_env = Environment.current
+        Environment.current = self
+        return self
+
+    def __exit__(self, ptype, value, trace):
+        Environment.current = self._last_env
 
     def pkg_config(self):
         """PkgConfig instance"""

vta/tests/python/unittest/test_environment.py

@@ -6,6 +6,15 @@ def test_env():
     mock = env.mock
     assert mock.alu == "skip_alu"
 
+def test_env_scope():
+    env = vta.get_env()
+    cfg = env.pkg_config().cfg_dict
+    cfg["TARGET"] = "xyz"
+    with vta.Environment(cfg):
+        assert vta.get_env().TARGET == "xyz"
+    assert vta.get_env().TARGET == env.TARGET
+
 
 if __name__ == "__main__":
     test_env()
+    test_env_scope()