py3.7 fix

PyUnicode_AsUTF8() returns const char* in py3.7 instead of char*. Making
changes to reflect that which should also be safe in
other Python versions.

src/Base/PyObjectBase.cpp

@@ -141,7 +141,7 @@ PyMethodDef PyObjectBase::Methods[] = {
 
 PyObject* PyObjectBase::__getattro(PyObject * obj, PyObject *attro)
 {
-    char *attr;
+    const char *attr;
 #if PY_MAJOR_VERSION >= 3
     attr = PyUnicode_AsUTF8(attro);
 #else
@@ -195,7 +195,7 @@ PyObject* PyObjectBase::__getattro(PyObject * obj, PyObject *attro)
 
 int PyObjectBase::__setattro(PyObject *obj, PyObject *attro, PyObject *value)
 {
-    char *attr;
+    const char *attr;
 #if PY_MAJOR_VERSION >= 3
     attr = PyUnicode_AsUTF8(attro);
 #else
@@ -236,7 +236,7 @@ int PyObjectBase::__setattro(PyObject *obj, PyObject *attro, PyObject *value)
 /*------------------------------
  * PyObjectBase attributes	-- attributes
 ------------------------------*/
-PyObject *PyObjectBase::_getattr(char *attr)
+PyObject *PyObjectBase::_getattr(const char *attr)
 {
     if (streq(attr, "__class__")) {
         // Note: We must return the type object here, 
@@ -279,7 +279,7 @@ PyObject *PyObjectBase::_getattr(char *attr)
     }
 }
 
-int PyObjectBase::_setattr(char *attr, PyObject *value)
+int PyObjectBase::_setattr(const char *attr, PyObject *value)
 {
     if (streq(attr,"softspace"))
         return -1; // filter out softspace

src/Base/PyObjectBase.h

@@ -231,7 +231,7 @@ public:
      *  need to call the method of the base class! Otherwise even the 
      *  methods of the object will disappear!
      */
-    virtual PyObject *_getattr(char *attr);
+    virtual PyObject *_getattr(const char *attr);
     /// static wrapper for pythons _getattro()
     static  PyObject *__getattro(PyObject * PyObj, PyObject *attro);
 
@@ -241,7 +241,7 @@ public:
      *  this method.
      *  You have to call the method of the base class.
      */
-    virtual int _setattr(char *attro, PyObject *value);    // _setattr method
+    virtual int _setattr(const char *attro, PyObject *value);    // _setattr method
     /// static wrapper for pythons _setattro(). // This should be the entry in Type. 
     static  int __setattro(PyObject *PyObj, PyObject *attro, PyObject *value);