Now passing strings to mimetypes.guess_extension.

Also changing the default extension to .dat (from None).

Also, whatever was originally implementing mime2extension did not include
the leading dot that mimetypes includes.  We are doing away with that, too.

This is supposed to address bug #552.

CHANGES.rst

@@ -1,6 +1,12 @@
 1.6 (unreleased)
 ================
 
+Bug Fixes
+---------
+
+- cachedataset() and friends again produce reasonable file extensions.
+  [#553]
+
 Enhancements and Fixes
 ----------------------
 
@@ -23,7 +29,7 @@ Enhancements and Fixes
   them. [#517]
 
 - Introducing the new MIVOT module, enabling processed VOTable data mapped to
-  any model serialized in VO-DML. This package dynamically generates python objects 
+  any model serialized in VO-DML. This package dynamically generates python objects
   whose structure corresponds to the classes of the mapped models. [#497]
 
 Deprecations and Removals

pyvo/dal/adhoc.py

@@ -167,7 +167,7 @@ def get_adhocservice_by_id(self, id_):
 
 class DatalinkResultsMixin(AdhocServiceResultsMixin):
     """
-    Mixin for datalink functionallity for results classes.
+    Mixin for datalink functionality for results classes.
     """
 
     def iter_datalinks(self):
@@ -486,7 +486,13 @@ class DatalinkResults(DatalinkResultsMixin, DALResults):
     argument is a string, it is interpreted as the name of a column,
     and the data from the column matching that name is returned as
     a Numpy array.
+
+    Where DatalinkResult instances were created from result table rows,
+    the row the DatalinkResult was generated from is available as
+    `original_row`.  DatalinkResult instances generated by other means
+    have a ``None`` here.
     """
+    original_row = None
 
     def getrecord(self, index):
         """
@@ -629,6 +635,15 @@ def get_first_proc(self):
             return proc
         raise IndexError("No processing service found in datalink result")
 
+    def set_original_row(self, row):
+        """
+        note the table row this DatalinkResults instance was generated
+        from.
+
+        This is mostly for pyVO-internal use.
+        """
+        self.original_row = row
+
 
 class SodaRecordMixin:
     """

pyvo/dal/mimetype.py

@@ -25,8 +25,11 @@ def mime2extension(mimetype, default=None):
     implementations of ``suggest_extension()`` in ``Record`` subclasses.
 
       >>> mime2extension('application/fits')
+      'fits'
       >>> mime2extension('image/jpeg')
+      'jpg'
       >>> mime2extension('application/x-zed', 'dat')
+      'dat'
 
     Parameters
     ----------
@@ -46,11 +49,14 @@ def mime2extension(mimetype, default=None):
     if not mimetype:
         return default
 
-    if isinstance(mimetype, str):
-        mimetype = mimetype.encode('utf-8')
+    if isinstance(mimetype, bytes):
+        mimetype = mimetype.decode('utf-8')
 
     ext = mimetypes.guess_extension(mimetype, strict=False)
-    return ext
+    if ext is None:
+        return default
+
+    return ext.lstrip(".")
 
 
 def mime_object_maker(url, mimetype, *, session=None):

pyvo/dal/sia.py

@@ -903,7 +903,7 @@ def suggest_dataset_basename(self):
             out = re.sub(r'\s+', '_', out.strip())
         return out
 
-    def suggest_extension(self, *, default=None):
+    def suggest_extension(self, *, default='dat'):
         """
         returns a recommended filename extension for the dataset described
         by this record.  Typically, this would look at the column describing