Enable checking of "untyped defs" and fix types

`set_key` and `unset_key` were more restrictive than other functions
such as `dotenv_values` with regards to their `dotenv_path` argument.

CHANGELOG.md

@@ -7,6 +7,11 @@ project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
+### Added
+
+- The `dotenv_path` argument of `set_key` and `unset_key` now has a type of `Union[str,
+  os.PathLike]` instead of just `os.PathLike` (#347 by [@bbc2]).
+
 ### Changed
 
 - Require Python 3.5 or a later version.  Python 2 and 3.4 are no longer supported. (#341

setup.cfg

@@ -14,6 +14,7 @@ max-line-length = 120
 exclude = .tox,.git,docs,venv,.venv
 
 [mypy]
+check_untyped_defs = true
 ignore_missing_imports = true
 
 [metadata]

src/dotenv/main.py

@@ -114,7 +114,7 @@ def get_key(dotenv_path: Union[str, _PathLike], key_to_get: str) -> Optional[str
 
 
 @contextmanager
-def rewrite(path: _PathLike) -> Iterator[Tuple[IO[str], IO[str]]]:
+def rewrite(path: Union[str, _PathLike]) -> Iterator[Tuple[IO[str], IO[str]]]:
     try:
         if not os.path.isfile(path):
             with io.open(path, "w+") as source:
@@ -131,7 +131,7 @@ def rewrite(path: _PathLike) -> Iterator[Tuple[IO[str], IO[str]]]:
 
 
 def set_key(
-    dotenv_path: _PathLike,
+    dotenv_path: Union[str, _PathLike],
     key_to_set: str,
     value_to_set: str,
     quote_mode: str = "always",
@@ -175,7 +175,7 @@ def set_key(
 
 
 def unset_key(
-    dotenv_path: _PathLike,
+    dotenv_path: Union[str, _PathLike],
     key_to_unset: str,
     quote_mode: str = "always",
 ) -> Tuple[Optional[bool], str]: