On RHEL7 the python3 binary is actually naed python3.4.
The usual python3 is not available there.
Searching explicitly for python3.4 amongst the others will fix the issue.

https://github.com/DinoTools/dionaea/pull/180
diff -ru dionaea-d2efb768e753a7f1ddca6dbf402548d741f33574.orig/configure.ac dionaea-d2efb768e753a7f1ddca6dbf402548d741f33574.new/configure.ac
--- dionaea-d2efb768e753a7f1ddca6dbf402548d741f33574.orig/configure.ac	2018-03-26 21:49:11.042568472 +0200
+++ dionaea-d2efb768e753a7f1ddca6dbf402548d741f33574.new/configure.ac	2018-03-26 21:49:29.854553159 +0200
@@ -580,7 +580,7 @@
 				      [cython_dir="$withval"],[cython_dir=$PATH])
 
 if test x$enable_cython = "xyes" ; then
-	AC_PATH_PROGS(CYTHON_BIN, [cython3 cython], "no", $cython_dir)
+	AC_PATH_PROGS(CYTHON_BIN, [cython3.4 cython3 cython], "no", $cython_dir)
 	if test "x$CYTHON_BIN" == "xno" ; then
 		enable_cython="no"
 	fi