blocks(): check if one of {blocksize, out} is specified

pysoundfile.py

@@ -746,7 +746,10 @@ def blocks(self, blocksize=None, overlap=0, frames=-1, dtype='float64',
         if self.mode == 'w':
             raise RuntimeError("blocks() is not allowed in write mode")
 
-        if out is not None:
+        if out is None:
+            if blocksize is None:
+                raise TypeError("One of {blocksize, out} must be specified")
+        else:
             if blocksize is not None:
                 raise TypeError(
                     "Only one of {blocksize, out} may be specified")

tests/test_pysoundfile.py

@@ -206,6 +206,11 @@ def assert_equal_list_of_arrays(list1, list2):
         assert np.all(item1 == item2)
 
 
+def test_blocks_without_blocksize():
+    with pytest.raises(TypeError):
+        list(sf.blocks(filename_stereo))
+
+
 def test_blocks_full_last_block():
     blocks = list(sf.blocks(filename_stereo, blocksize=2))
     assert_equal_list_of_arrays(blocks, [data_stereo[0:2], data_stereo[2:4]])
@@ -241,7 +246,7 @@ def test_blocks_with_stop():
 
 
 def test_blocks_with_too_large_start():
-    blocks = list(sf.blocks(filename_stereo, start=666))
+    blocks = list(sf.blocks(filename_stereo, blocksize=2, start=666))
     assert_equal_list_of_arrays(blocks, [[]])