Revert "Drop support for Python 3.6. (#150)" (#154)

This reverts commit 7b7df8f.

Author: bjlittle

.cirrus.yml

@@ -88,6 +88,8 @@ test_task:
   only_if: ${SKIP_TEST_TASK} == ""
   auto_cancellation: true
   matrix:
+    env:
+      PY_VER: "3.6"
     env:
       PY_VER: "3.7"
     env:

noxfile.py

@@ -22,7 +22,7 @@
 PACKAGE = "esmf_regrid"
 
 #: Cirrus-CI environment variable hook.
-PY_VER = os.environ.get("PY_VER", ["3.7", "3.8"])
+PY_VER = os.environ.get("PY_VER", ["3.6", "3.7", "3.8"])
 
 #: Cirrus-CI environment variable hook.
 COVERAGE = os.environ.get("COVERAGE", False)

requirements/nox.lock/py36-linux-64.lock

@@ -0,0 +1,30 @@
+name: esmf-regrid-dev
+
+channels:
+  - conda-forge
+
+dependencies:
+  - python=3.6
+
+# Setup dependencies.
+  - setuptools>=40.8.0
+
+# Core dependencies.
+  - cartopy>=0.18
+  - numpy>=1.14
+  - scipy
+  - esmpy>=7.0
+  - iris
+  - cf-units
+
+# Test dependencies.
+  - asv
+  - black=20.8b1
+  - codecov
+  - flake8
+  - flake8-docstrings
+  - flake8-import-order
+  - nox
+  - pre-commit
+  - pytest
+  - pytest-cov

requirements/nox.lock/py37-linux-64.lock

@@ -8,6 +8,7 @@ classifiers =
     Natural Language :: English
     Operating System :: OS Independent
     Programming Language :: Python :: 3
+    Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
     Topic :: Scientific/Engineering :: Atmospheric Science
@@ -29,7 +30,7 @@ version = attr: esmf_regrid.__version__
 [options]
 packages = find:
 python_requires =
-    >=3.7,<3.9
+    >=3.6,<3.9
 setup_requires =
     setuptools>=40.8.0
 zip_safe = False