improve eval_ToString

Author: mmatera

mathics/builtin/atomic/strings.py

@@ -282,17 +282,14 @@ def eval_set(self, value, evaluation):
 
     def eval_setdelayed(self, value, evaluation):
         """SetDelayed[$CharacterEncoding, value_]"""
-        if (
-            not isinstance(value, String)
-            or value.value not in CHARACTER_ENCODING_MAP.keys()
-        ):
+        if not isinstance(value, String):
             evaluation.message("$CharacterEncoding", "charcode", value)
             return
         try:
             load_encoding_table(value.value, evaluation)
             evaluation.definitions.set_ownvalue("System`$CharacterEncoding", value)
         except EncodingNameError:
-            pass
+            evaluation.message("$CharacterEncoding", "charcode", value)
 
 
 class CharacterEncodings(Predefined):

mathics/eval/strings.py

@@ -26,12 +26,16 @@ def eval_ToString(
 ) -> String:
 
     boxes = format_element(expr, evaluation, form)
-
-    if encoding not in ("utf8", "utf-8", "unicode"):
-        try:
-            load_encoding_table(encoding, evaluation)
-        except EncodingNameError:
-            return String(boxes.to_text(evaluation=evaluation, encoding="Unicode"))
+    try:
+        return String(boxes.to_text(evaluation=evaluation, encoding=encoding))
+    except EncodingNameError:
+        pass
+
+    # If the encoding does not already exists, try to load it and do it again.
+    try:
+        load_encoding_table(encoding, evaluation)
+    except EncodingNameError:
+        return String(boxes.to_text(evaluation=evaluation, encoding="Unicode"))
 
     return String(boxes.to_text(evaluation=evaluation, encoding=encoding))