Fix empty and non-advancing chunk ranges

boltons/iterutils.py

@@ -366,6 +366,8 @@ def chunk_ranges(input_size, chunk_size, input_offset=0, overlap_size=0, align=F
     are always at the beginning of the chunk.
 
     Returns an iterator of (start, end) tuples, one tuple per chunk.
+    An empty input yields no chunks. *overlap_size* must be less than
+    *chunk_size*, so each chunk advances through the input.
 
     >>> list(chunk_ranges(input_offset=10, input_size=10, chunk_size=5))
     [(10, 15), (15, 20)]
@@ -394,6 +396,11 @@ def chunk_ranges(input_size, chunk_size, input_offset=0, overlap_size=0, align=F
     overlap_size = _validate_positive_int(
         overlap_size, 'overlap_size', strictly_positive=False)
 
+    if overlap_size >= chunk_size:
+        raise ValueError('overlap_size must be less than chunk_size')
+    if input_size == 0:
+        return
+
     input_stop = input_offset + input_size
 
     if align:

tests/test_iterutils.py

@@ -697,3 +697,20 @@ def test_frange_xfrange_zero_step():
         frange(10, step=0)
     with pytest.raises(ValueError):
         list(xfrange(10, step=0))
+
+
+@pytest.mark.parametrize('align', [False, True])
+@pytest.mark.parametrize('input_offset', [0, 1, 4, 10])
+def test_chunk_ranges_empty(align, input_offset):
+    from boltons.iterutils import chunk_ranges
+
+    assert list(chunk_ranges(0, 5, input_offset=input_offset, align=align)) == []
+
+
+@pytest.mark.parametrize('align', [False, True])
+@pytest.mark.parametrize('overlap_size', [5, 6, 10])
+def test_chunk_ranges_invalid_overlap(align, overlap_size):
+    from boltons.iterutils import chunk_ranges
+
+    with pytest.raises(ValueError, match='overlap_size.*chunk_size'):
+        list(chunk_ranges(12, 5, overlap_size=overlap_size, align=align))