ENH: Add and use cmake flag DISABLE_PYTHON

Also, undo previous commit per discussion at
#217

Author: Lee Newberg

CMakeLists.txt

@@ -66,6 +66,7 @@ option(ENABLE_TESTS "Enable build tests for EXP, pyEXP and helpers" ON)
 option(ENABLE_MINIMAL "Compile EXP support libraries only" OFF)
 option(BUILD_SHARED_LIBS "Build using shared libraries" ON)
 option(BUILD_DOCS "Build documentation" OFF)
+option(DISABLE_PYTHON "Disable the Python development environment" OFF)
 
 # Metaflag for minimal build
 
@@ -298,13 +299,15 @@ if(ENABLE_TESTS)
   add_subdirectory(tests)
 endif()
 
-if(ENABLE_PYEXP)
-  # try to find pybind11 and build wrapper python module
+# try to find pybind11 and build wrapper python module
+if (NOT DISABLE_PYTHON)
   find_package(Python3 COMPONENTS Interpreter Development)
-  message(STATUS "python3 include dirs: ${Python3_INCLUDE_DIRS}")
-  if(Python3_FOUND)
-    set(HAVE_PYTHON3 TRUE)
-  else()
+endif()
+message(STATUS "python3 include dirs: ${Python3_INCLUDE_DIRS}")
+if(Python3_FOUND)
+  set(HAVE_PYTHON3 TRUE)
+else()
+  if(ENABLE_PYEXP)
     message(FATAL_ERROR "You asked for pyEXP but I cannot find a Python3 environment. Please make Python3 available or disable pyEXP. CMake will exit." )
   endif()
 endif()

exputil/DiskDensityFunc.cc

@@ -1,4 +1,3 @@
-#include <stdexcept>
 #include "DiskDensityFunc.H"
 
 #ifdef HAVE_PYTHON3

include/DiskDensityFunc.H

@@ -2,11 +2,9 @@
 #define _DiskDensityFunc_H_
 
 #include <functional>
-#include <string>
 
 #include "config_exp.h"
 
-#ifdef HAVE_PYTHON3
 #include <pybind11/pybind11.h>
 #include <pybind11/embed.h>
 
@@ -28,14 +26,12 @@
         a = 1.0                            # Scale radius
         h = 0.2                            # Scale height
         f = math.exp(-0.5*math.fabs(z)/h)  # Prevent overflows
-        sech = 2.0*f / (1.0 + f*f)         #
+        sech = 2.0*f / (1.0 + f*f)         # 
         return math.exp(-R/a)*sech*sech/(8*math.pi*h*a*a)
-
+	
     --------------------------cut here--------------------------------
 
  */
-#endif
-
 class __attribute__((visibility("default")))
 DiskDensityFunc
 {