Merge pull request #46 from IAMconsortium/fix/py37

Add typing_extensions to py3.7 deps for Literal

.github/workflows/test.yaml

@@ -29,6 +29,7 @@ jobs:
 
     - uses: actions/setup-python@v4
       with:
+        python-version: "3.x"
         cache: pip
         cache-dependency-path: "**/pyproject.toml"
 

iam_units/currency.py

@@ -3,7 +3,13 @@
 See the inline comments (NB) for possible extensions of this code; also
 iam_units.update.currency.
 """
-from typing import Literal, Union
+from typing import Union
+
+try:
+    from typing import Literal
+except ImportError:
+    from typing_extensions import Literal  # type: ignore [assignment]
+
 
 #: Exchange rate data for method=EXC, period=2005, from
 #: https://data.oecd.org/conversion/exchange-rates.htm

pyproject.toml

@@ -25,7 +25,7 @@ classifiers = [
   "Topic :: Scientific/Engineering",
   "Topic :: Scientific/Engineering :: Information Analysis",
 ]
-dependencies = ["pint >= 0.11"]
+dependencies = ["pint >= 0.11", "typing_extensions; python_version < '3.8'"]
 
 [project.urls]
 homepage = "https://github.com/IAMconsortium/units"