fix a bug that makes that URLSave always fails

mathics/builtin/files_io/files.py

@@ -1696,13 +1696,15 @@ class Write(Builtin):
     def apply(self, channel, expr, evaluation):
         "Write[channel_, expr___]"
 
-        strm = channel_to_stream(channel)
+        stream = None
+        if isinstance(channel, String):
+            stream = {"stdout": 1, "stderr": 2}.get(channel.value, None)
 
-        if strm is None:
-            return
-
-        n = strm.elements[1].get_int_value()
-        stream = stream_manager.lookup_stream(n)
+        if stream is None:
+            strm = channel_to_stream(channel, "w")
+            if strm is None:
+                return
+            stream = stream_manager.lookup_stream(strm.elements[1].get_int_value())
 
         if stream is None or stream.io is None or stream.io.closed:
             evaluation.message("General", "openx", channel)
@@ -1763,6 +1765,9 @@ class WriteString(Builtin):
     #> DeleteFile[pathname];
     #> Clear[pathname];
 
+
+    If stream is the string "stdout" or "stderr", writes to the system standard output/ standard error channel:
+    >> WriteString["stdout", "Hola"]
     """
 
     summary_text = "write a sequence of strings to a stream, with no extra newlines"
@@ -1773,12 +1778,18 @@ class WriteString(Builtin):
 
     def apply(self, channel, expr, evaluation):
         "WriteString[channel_, expr___]"
-        strm = channel_to_stream(channel, "w")
-
-        if strm is None:
-            return
-
-        stream = stream_manager.lookup_stream(strm.elements[1].get_int_value())
+        stream = None
+        if isinstance(channel, String):
+            if channel.value == "stdout":
+                stream = stream_manager.lookup_stream(1)
+            elif channel.value == "stderr":
+                stream = stream_manager.lookup_stream(2)
+
+        if stream is None:
+            strm = channel_to_stream(channel, "w")
+            if strm is None:
+                return
+            stream = stream_manager.lookup_stream(strm.elements[1].get_int_value())
 
         if stream is None or stream.io is None or stream.io.closed:
             return None

mathics/builtin/files_io/filesystem.py

@@ -2274,7 +2274,7 @@ def apply_2(self, url, filename, evaluation, **options):
         url = url.value
         if filename is None:
             result = urlsave_tmp(url, None, **options)
-        elif filename.get_head_name() == "String":
+        elif isinstance(filename, String):
             filename = filename.value
             result = urlsave_tmp(url, filename, **options)
         else:

mathics/core/streams.py

@@ -43,9 +43,10 @@ def urlsave_tmp(url, location=None, **kwargs):
             with open(location, "wb") as fp:
                 fp.write(r.content)
                 result = fp.name
+            return result
         except Exception:
-            result = None
-    return result
+            return None
+    return None
 
 
 def path_search(filename: str) -> Tuple[str, bool]: