PY37: Use typing_extensions to get Literal in Python 3.7

Author: effigies

pydra/tasks/core/sequences.py

@@ -4,10 +4,15 @@
 from pydra.engine.core import TaskBase
 from pydra.engine.helpers import ensure_list
 
+try:
+    from typing import Literal
+except ImportError:  # PY37
+    from typing_extensions import Literal
+
 
 @attr.s(kw_only=True)
 class MergeInputSpec(BaseSpec):
-    axis: ty.Literal["vstack", "hstack"] = attr.ib(
+    axis: Literal["vstack", "hstack"] = attr.ib(
         default="vstack",
         metadata={
             "help_string": "Direction in which to merge, hstack requires same number of elements in each input."

setup.cfg

@@ -28,6 +28,7 @@ install_requires =
     cloudpickle >= 1.2.2
     filelock >= 3.0.0
     etelemetry >= 0.2.2
+    typing_extensions ; python_version < "3.8"
 
 test_requires =
     pytest >= 4.4.0, < 6.0.0