Fix type hint for _stdlib style arg (#77)

* Fix type hint for _stdlib `style` arg

* Add typing_extensions for <py3.8

* More mypy fixes

* Ignore missing Literal

Author: basepi

.pre-commit-config.yaml

@@ -15,7 +15,7 @@ repos:
     rev: v0.910
     hooks:
     -   id: mypy
-        args: [--strict, --show-error-codes, --no-warn-unused-ignores]
+        args: [--strict, --show-error-codes, --no-warn-unused-ignores, --implicit-reexport]
 -   repo: https://github.com/ambv/black
     rev: 21.6b0
     hooks:

ecs_logging/_stdlib.py

@@ -33,6 +33,11 @@
 if TYPE_CHECKING:
     from typing import Optional, Any, Callable, Dict, Sequence
 
+    try:
+        from typing import Literal, Union  # type: ignore
+    except ImportError:
+        from typing_extensions import Literal, Union  # type: ignore
+
 
 # Load the attributes of a LogRecord so if some are
 # added in the future we won't mistake them for 'extra=...'
@@ -75,7 +80,7 @@ def __init__(
         self,  # type: Any
         fmt=None,  # type: Optional[str]
         datefmt=None,  # type: Optional[str]
-        style="%",  # type: str
+        style="%",  # type: Union[Literal["%"], Literal["{"], Literal["$"]]
         validate=None,  # type: Optional[bool]
         stack_trace_limit=None,  # type: Optional[int]
         extra=None,  # type: Optional[Dict[str, Any]]