Install typing_extensions if needed

The `typing_extensions` module was imported but not listed as a
requirement, so importing `daidepp` failed if `typing_extensions` wasn't
installed for another reason.

I have added it as an explicit requirement and only use it if `Literal`
or `get_args` cannot be imported directly from the `typing` module.

Author: aphedges

setup.cfg

@@ -15,6 +15,7 @@ python_requires = >=3.7
 install_requires =
     parsimonious==0.9.0
     importlib-metadata>=1.4.0 ; python_version < "3.8"
+    typing_extensions>=3.10.0.0 ; python_version < "3.8"
 
 [options.packages.find]
 where = src

src/daidepp/constants.py

@@ -1,4 +1,7 @@
-from typing_extensions import Literal
+try:
+    from typing import Literal
+except ImportError:
+    from typing_extensions import Literal
 
 Power = Literal["AUS", "ENG", "FRA", "GER", "ITA", "RUS", "TUR"]
 UnitType = Literal["AMY", "FLT"]

src/daidepp/grammar/grammar.py

@@ -5,9 +5,13 @@
 from __future__ import annotations
 
 from typing import Dict, Tuple
-from typing_extensions import get_args
 
-from typing_extensions import Literal
+try:
+    from typing import Literal
+    from typing import get_args
+except ImportError:
+    from typing_extensions import Literal
+    from typing_extensions import get_args
 
 DAIDELevel = Literal[
     0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160

src/daidepp/grammar/grammar_utils.py

@@ -3,7 +3,11 @@
 from typing import Dict, List, Optional, Set, Tuple, Union
 
 from parsimonious.grammar import Grammar
-from typing_extensions import Literal
+
+try:
+    from typing import Literal
+except ImportError:
+    from typing_extensions import Literal
 
 from daidepp.constants import PressKeywords
 from daidepp.grammar.grammar import (

src/daidepp/keywords/base_keywords.py

@@ -3,7 +3,10 @@
 from dataclasses import dataclass
 from typing import Optional, Tuple, Union
 
-from typing_extensions import get_args
+try:
+    from typing import get_args
+except ImportError:
+    from typing_extensions import get_args
 
 from daidepp.constants import *
 from daidepp.keywords.daide_object import _DAIDEObject

src/daidepp/visitor.py

@@ -2,7 +2,11 @@
 from typing import Any
 
 from parsimonious.nodes import Node, NodeVisitor
-from typing_extensions import get_args
+
+try:
+    from typing import get_args
+except ImportError:
+    from typing_extensions import get_args
 
 from daidepp.constants import ProvinceNoCoast
 from daidepp.keywords.base_keywords import *

tests/conftest.py

@@ -1,5 +1,9 @@
 import pytest
-from typing_extensions import get_args
+
+try:
+    from typing import get_args
+except ImportError:
+    from typing_extensions import get_args
 
 from daidepp.grammar import create_daide_grammar
 from daidepp.grammar.grammar import DAIDELevel, MAX_DAIDE_LEVEL