Perform sanity checks on Python3

Makefile

@@ -1,3 +1,4 @@
+include mk/python.mk
 DCURL_DIR := deps/dcurl
 DCURL_LIB := $(DCURL_DIR)/build/libdcurl.so
 DEPS += $(DCURL_LIB)
@@ -19,7 +20,7 @@ TESTS += $(wildcard tests/tangleid/*.sh)
 check: server.py $(DCURL_LIB)
 	@ TMP_PID=`mktemp /tmp/server_pid.XXXXXX`; \
 	echo "Running test suite..." ; \
-	( python $^ & echo $$! > $${TMP_PID} ); \
+	( $(PYTHON) $^ & echo $$! > $${TMP_PID} ); \
 	sleep 3 ; \
 	for i in $(TESTS); do \
 	    ( echo "\n\n==[ $$i ]==\n"; $$i || kill -9 `cat $${TMP_PID}` ) \

mk/python.mk

@@ -0,0 +1,12 @@
+PYTHON = python3
+PYTHON := $(shell which $(PYTHON))
+ifndef PYTHON
+$(error "python3 is required.")
+endif
+
+# check "iota" module in Python installation
+PY_CHECK_MOD_IOTA := $(shell $(PYTHON) -c "import iota" 2>/dev/null && \
+                       echo 1 || echo 0)
+ifneq ("$(PY_CHECK_MOD_IOTA)","1")
+    $(error "skip $@ because PyOTA is not installed.")
+endif