Exclude pandas installation for Python < 3.7

numpy, a pandas dependency, required Python > 3.7 as of version 1.20.0.
Hence, case_sparql_select cannot import pandas in a Python 3.6
environment.

This patch adds steps to disable dependency installation and tests for
case_sparql_select if Python is detected to be < 3.7.x.

As a reminder, Python 3.6 goes EOL on 2021-12-23.  By or at that time,
3.6 will be removed from this project.

References:
* [AC-178] Add website repository's sample runner to
  CASE-Utilities-Python repository
* [PEP-0494] https://www.python.org/dev/peps/pep-0494/#and-beyond-schedule
* [numpy 1.20.0] https://pypi.org/project/numpy/1.20.0/

Signed-off-by: Alex Nelson <alexander.nelson@nist.gov>

Author: ajnelson-nist

README.md

@@ -62,6 +62,8 @@ case_sparql_select output.html input.sparql input.json [input-2.json ...]
 case_sparql_select output.md input.sparql input.json [input-2.json ...]
 ```
 
+Note that `case_sparql_select` is not guaranteed to function with Pythons below version 3.7.
+
 
 ### `local_uuid`
 

setup.cfg

@@ -18,7 +18,8 @@ classifiers =
 # TODO The constraint on pyparsing can be removed when rdflib Issue #1190 is resolved.
 # https://github.com/RDFLib/rdflib/issues/1190
 install_requires =
-    pandas
+    # Note that numpy (pandas dependency) is only supported in Python >= 3.7.
+    pandas;python_version>='3.7'
     pyparsing < 3.0.0
     rdflib-jsonld
     requests
@@ -30,4 +31,5 @@ python_requires = >=3.6
 console_scripts =
     case_file = case_utils.case_file:main
     case_sparql_construct = case_utils.case_sparql_construct:main
+    # Note that numpy (pandas dependency, and pandas is dependency of case_sparql_select) is only supported in Python >= 3.7.
     case_sparql_select = case_utils.case_sparql_select:main

tests/Makefile

@@ -73,8 +73,11 @@ all-case_sparql_construct: \
 
 all-case_sparql_select: \
   .venv.done.log
-	$(MAKE) \
-	  --directory case_sparql_select
+	# Only descend if python>=3.7, due to pandas dependency unsatisfiable in 3.6.x.
+	# Boolean explanation: sys.exit(False) has exit status 0.
+	venv/bin/python3 -c 'import sys ; sys.exit(not (sys.version_info < (3, 7)))' \
+	  || $(MAKE) \
+	    --directory case_sparql_select
 
 # These check calls are provided in preferred run-order.
 check: \
@@ -103,9 +106,12 @@ check-case_sparql_construct: \
 
 check-case_sparql_select: \
   .venv.done.log
-	$(MAKE) \
-	  --directory case_sparql_select \
-	  check
+	# Only descend if python>=3.7, due to pandas dependency unsatisfiable in 3.6.x.
+	# Boolean explanation: sys.exit(False) has exit status 0.
+	venv/bin/python3 -c 'import sys ; sys.exit(not (sys.version_info < (3, 7)))' \
+	  || $(MAKE) \
+	    --directory case_sparql_select \
+	    check
 
 check-isomorphic_diff: \
   .venv.done.log