feat(set_env): add set_env contextmanager utility (#87)

modflow_devtools/misc.py

@@ -29,6 +29,39 @@ def set_dir(path: PathLike):
         print(f"Returned to previous directory: {origin}")
 
 
+@contextmanager
+def set_env(*remove, **update):
+    """
+    Temporarily updates the ``os.environ`` dictionary in-place.
+
+    Referenced from https://stackoverflow.com/a/34333710/6514033.
+
+    The ``os.environ`` dictionary is updated in-place so that the modification
+    is sure to work in all situations.
+
+    :param remove: Environment variables to remove.
+    :param update: Dictionary of environment variables and values to add/update.
+    """
+    env = environ
+    update = update or {}
+    remove = remove or []
+
+    # List of environment variables being updated or removed.
+    stomped = (set(update.keys()) | set(remove)) & set(env.keys())
+    # Environment variables and values to restore on exit.
+    update_after = {k: env[k] for k in stomped}
+    # Environment variables and values to remove on exit.
+    remove_after = frozenset(k for k in update if k not in env)
+
+    try:
+        env.update(update)
+        [env.pop(k, None) for k in remove]
+        yield
+    finally:
+        env.update(update_after)
+        [env.pop(k) for k in remove_after]
+
+
 class add_sys_path:
     """
     Context manager for temporarily editing the system path

modflow_devtools/test/test_misc.py

@@ -11,6 +11,7 @@
     get_packages,
     has_package,
     set_dir,
+    set_env,
 )
 
 
@@ -21,6 +22,22 @@ def test_set_dir(tmp_path):
     assert Path(os.getcwd()) != tmp_path
 
 
+def test_set_env(tmp_path):
+    # test adding a variable
+    key = "TEST_ENV"
+    val = "test"
+    assert environ.get(key) is None
+    with set_env(**{key: val}):
+        assert environ.get(key) == val
+    with set_env(TEST_ENV=val):
+        assert environ.get(key) == val
+
+    # test removing a variable
+    with set_env(**{key: val}):
+        with set_env(key):
+            assert environ.get(key) is None
+
+
 _repos_path = environ.get("REPOS_PATH")
 if _repos_path is None:
     _repos_path = Path(__file__).parent.parent.parent.parent