Fix filldown RuntimeError on header-only tables

docs/changes.rst

@@ -6,6 +6,11 @@ Version 1.7.17
 
 ## Whats Changed
 
+* Fix: :func:`petl.transform.fills.filldown` raised ``RuntimeError`` on a
+  header-only table (one with no data rows), whereas :func:`fillright` and
+  :func:`fillleft` return the header unchanged.
+  By :user:`sarathfrancis90`, :issue:`698`.
+
 * ci: added readthedocs settings file
   By :user:`juarezr`, :issue:`677`.
 

petl/test/transform/test_fills.py

@@ -60,6 +60,19 @@ def test_filldown_headerless():
     ieq(expect, actual)
 
 
+def test_filldown_header_only():
+    table = (('foo', 'bar', 'baz'),)
+    expect = (('foo', 'bar', 'baz'),)
+
+    actual = filldown(table)
+    ieq(expect, actual)
+    ieq(expect, actual)
+
+    actual = filldown(table, 'bar')
+    ieq(expect, actual)
+    ieq(expect, actual)
+
+
 def test_fillright():
 
     table = (('foo', 'bar', 'baz'),

petl/transform/fills.py

@@ -112,7 +112,10 @@ def iterfilldown(table, fillfields, missing):
     if not fillfields:  # fill down all fields
         fillfields = hdr
     fillindices = asindices(hdr, fillfields)
-    fill = list(next(it))  # fill values
+    try:
+        fill = list(next(it))  # fill values
+    except StopIteration:
+        return
     yield tuple(fill)
     for row in it:
         outrow = list(row)