Fix Tools/scripts/generate_opcode_h.py from issue #17861 to work correctly

when building in a separate object tree. More people should build this way.
This may still fail if the source is unwritable, I haven't tested that yet.

Makefile.pre.in

@@ -324,10 +324,10 @@ PGENOBJS=	$(POBJS) $(PGOBJS)
 
 ##########################################################################
 # opcode.h generation
-OPCODE_H_DIR= 	Include
-OPCODE_H_SCRIPT= Tools/scripts/generate_opcode_h.py
-OPCODE_H=	$(srcdir)/$(OPCODE_H_DIR)/opcode.h
-OPCODE_H_GEN=	@OPCODEHGEN@  $(OPCODE_H_SCRIPT) Lib/ $(OPCODE_H)
+OPCODE_H_DIR= 	$(srcdir)/Include
+OPCODE_H_SCRIPT= $(srcdir)/Tools/scripts/generate_opcode_h.py
+OPCODE_H=	$(OPCODE_H_DIR)/opcode.h
+OPCODE_H_GEN=	@OPCODEHGEN@  $(OPCODE_H_SCRIPT) $(srcdir)/Lib/opcode.py $(OPCODE_H)
 #
 ##########################################################################
 # AST

Tools/scripts/generate_opcode_h.py

@@ -1,10 +1,6 @@
 # This script generates the opcode.h header file.
 
 import sys
-if len(sys.argv) > 0:
-    sys.path.insert(0, sys.argv[1])
-# Importing module from our given src directory.
-import opcode
 header = """/* Auto-generated by Tools/scripts/generate_opcode_h.py */
 #ifndef Py_OPCODE_H
 #define Py_OPCODE_H
@@ -37,17 +33,20 @@ enum cmp_op {PyCmp_LT=Py_LT, PyCmp_LE=Py_LE, PyCmp_EQ=Py_EQ, PyCmp_NE=Py_NE,
 """
 
 
-def main(outfile='Include/opcode.h'):
+def main(opcode_py, outfile='Include/opcode.h'):
+    opcode = {}
+    exec(open(opcode_py).read(), opcode)
+    opmap = opcode['opmap']
     with open(outfile, 'w') as fobj:
         fobj.write(header)
-        for name in opcode.opname:
-            if name in opcode.opmap:
-                fobj.write("#define %-20s\t%-3s\n" % (name, opcode.opmap[name]))
+        for name in opcode['opname']:
+            if name in opmap:
+                fobj.write("#define %-20s\t%-3s\n" % (name, opmap[name]))
             if name == 'POP_EXCEPT': # Special entry for HAVE_ARGUMENT
                 fobj.write("#define %-20s\t%-3d\n" %
-                            ('HAVE_ARGUMENT', opcode.HAVE_ARGUMENT))
+                            ('HAVE_ARGUMENT', opcode['HAVE_ARGUMENT']))
         fobj.write(footer)
 
 
 if __name__ == '__main__':
-    main(sys.argv[2])
+    main(sys.argv[1], sys.argv[2])