If possible don't required linking libpython

Summary: libpython linking has crept into many C++ binaries that were believed to be pure C++.  This has made for some confusing errors as we upgrade from python 3.10 -> 3.12.  This also causes the blast radius for python upgrades to affect countless C++ binaries that would otherwise not be affected.

Reviewed By: Gownta

Differential Revision: D72362668

fbshipit-source-id: 75b72552e91a71c656ea31c7e3474d42e8caab25

Author: fried

third-party/folly/src/folly/python/error.cpp

@@ -19,7 +19,7 @@
 #include <stdexcept>
 #include <string>
 
-#include <Python.h>
+#include <folly/python/Weak.h>
 
 #include <folly/Conv.h>
 #include <folly/ScopeGuard.h>
@@ -32,8 +32,8 @@ std::string pyObjectToString(PyObject* obj) {
   constexpr StringPiece kConversionFail = "Error conversion failed";
   PyObject *pyStr, *pyBytes;
   SCOPE_EXIT {
-    Py_XDECREF(pyStr);
-    Py_XDECREF(pyBytes);
+    Py_DecRef(pyStr);
+    Py_DecRef(pyBytes);
     // Swallow any errors that arise in this function
     PyErr_Clear();
   };
@@ -44,16 +44,12 @@ std::string pyObjectToString(PyObject* obj) {
   }
 
   char* cStr = nullptr;
-#if PY_VERSION_HEX < 0x0300000
-  cStr = PyString_AsString(pyStr);
-#else
   pyBytes = PyUnicode_AsEncodedString(pyStr, "utf-8", "strict");
   if (pyBytes == nullptr) {
     return std::string(kConversionFail);
   }
 
   cStr = PyBytes_AsString(pyBytes);
-#endif
 
   if (cStr == nullptr) {
     return std::string(kConversionFail);
@@ -67,9 +63,9 @@ std::string pyObjectToString(PyObject* obj) {
 void handlePythonError(StringPiece errPrefix) {
   PyObject *ptype, *pvalue, *ptraceback;
   SCOPE_EXIT {
-    Py_XDECREF(ptype);
-    Py_XDECREF(pvalue);
-    Py_XDECREF(ptraceback);
+    Py_DecRef(ptype);
+    Py_DecRef(pvalue);
+    Py_DecRef(ptraceback);
   };
   /**
    * PyErr_Fetch will clear the error indicator (which *should* be set here, but