Fix iterrowslice to conform with Python 3.7 PEP 479 which transforms …

…StopIteration in generators to RuntimeError exceptions

docs/changes.rst

@@ -4,6 +4,9 @@ Changes
 Version 1.7.8
 -------------
 
+* Fix iterrowslice() to conform with PEP 479
+  By :user:`arturponinski`, :issue:`575`.
+
 * Cleanup and unclutter old and unused files in repository
   By :user:`juarezr`, :issue:`606`.
 

petl/test/transform/test_basics.py

@@ -1,5 +1,6 @@
 from __future__ import absolute_import, print_function, division
 
+import pytest
 
 from petl.test.helpers import ieq
 from petl.util import expr, empty, coalesce
@@ -460,6 +461,20 @@ def test_head():
     ieq(expect, table2)
 
 
+def test_head_raises_stop_iteration_for_empty_table():
+    table = iter(head([]))
+    with pytest.raises(StopIteration):
+        next(table)  # header
+
+
+def test_head_raises_stop_iteration_for_header_only():
+    table1 = (('foo', 'bar', 'baz'),)
+    table = iter(head(table1))
+    next(table)  # header
+    with pytest.raises(StopIteration):
+        next(table)
+
+
 def test_tail():
 
     table1 = (('foo', 'bar'),

petl/transform/basics.py

@@ -727,7 +727,10 @@ def __iter__(self):
 
 def iterrowslice(source, sliceargs):
     it = iter(source)
-    yield tuple(next(it))  # fields
+    try:
+        yield tuple(next(it))  # fields
+    except StopIteration:
+        return
     for row in islice(it, *sliceargs):
         yield tuple(row)