WIP: read(): Don't ignore "frames" argument

Partial solution to #210, but this breaks blocks()!

The tests can be run without testing blocks():

    python3 -m pytest -k"not blocks"

soundfile.py

@@ -211,10 +211,10 @@ def read(file, frames=-1, start=0, stop=None, dtype='float64', always_2d=False,
         array anyway.
 
         If `out` was specified, it is returned.  If `out` has more
-        frames than available in the file (or if `frames` is smaller
-        than the length of `out`) and no `fill_value` is given, then
-        only a part of `out` is overwritten and a view containing all
-        valid frames is returned.
+        frames than available in the file and no `fill_value` is given,
+        or if `frames` is smaller than the length of `out`, then only a
+        part of `out` is overwritten and a view containing all valid
+        frames is returned.
     samplerate : int
         The sample rate of the audio file.
 
@@ -806,12 +806,11 @@ def read(self, frames=-1, dtype='float64', always_2d=False,
             one-dimensional array is returned. Use ``always_2d=True``
             to return a two-dimensional array anyway.
 
-            If `out` was specified, it is returned. If `out` has more
-            frames than available in the file (or if `frames` is
-            smaller than the length of `out`) and no `fill_value` is
-            given, then only a part of `out` is overwritten and a view
-            containing all valid frames is returned. numpy.ndarray or
-            type(out)
+            If `out` was specified, it is returned.  If `out` has more
+            frames than available in the file and no `fill_value` is
+            given, or if `frames` is smaller than the length of `out`,
+            then only a part of `out` is overwritten and a view
+            containing all valid frames is returned.
 
         Other Parameters
         ----------------
@@ -850,18 +849,25 @@ def read(self, frames=-1, dtype='float64', always_2d=False,
         buffer_read, .write
 
         """
+        explicit_frames = frames >= 0
+        if out is not None and (frames < 0 or frames > len(out)):
+            frames = len(out)
+        max_frames = self._check_frames(frames, fill_value)
         if out is None:
-            frames = self._check_frames(frames, fill_value)
-            out = self._create_empty_array(frames, always_2d, dtype)
-        else:
-            if frames < 0 or frames > len(out):
-                frames = len(out)
-        frames = self._array_io('read', out, frames)
-        if len(out) > frames:
+            out = self._create_empty_array(max_frames, always_2d, dtype)
+        read_frames = self._array_io('read', out, max_frames)
+        if read_frames < max_frames:
             if fill_value is None:
-                out = out[:frames]
+                # NB: This can only happen in non-seekable files
+                assert not self.seekable()
+                out = out[:read_frames]
+            else:
+                out[read_frames:max_frames] = fill_value
+        if max_frames < len(out):
+            if explicit_frames or fill_value is None:
+                out = out[:max_frames]
             else:
-                out[frames:] = fill_value
+                out[max_frames:] = fill_value
         return out
 
     def buffer_read(self, frames=-1, dtype=None):
@@ -1332,13 +1338,16 @@ def _prepare_read(self, start, stop, frames):
         if frames >= 0 and stop is not None:
             raise TypeError("Only one of {frames, stop} may be used")
 
+        explicit_stop = stop is not None
         start, stop, _ = slice(start, stop).indices(self.frames)
         if stop < start:
             stop = start
-        if frames < 0:
+        if explicit_stop:
             frames = stop - start
         if self.seekable():
             self.seek(start, SEEK_SET)
+        if frames < 0:
+            frames = self.frames - start
         return frames
 
 

tests/test_pysoundfile.py

@@ -364,8 +364,7 @@ def test_blocks_with_frames(file_stereo_r):
 def test_blocks_with_frames_and_fill_value(file_stereo_r):
     blocks = list(
         sf.blocks(file_stereo_r, blocksize=2, frames=3, fill_value=0))
-    last_block = np.row_stack((data_stereo[2:3], np.zeros((1, 2))))
-    assert_equal_list_of_arrays(blocks, [data_stereo[0:2], last_block])
+    assert_equal_list_of_arrays(blocks, [data_stereo[0:2], data_stereo[2:3]])
 
 
 def test_blocks_with_out(file_stereo_r):
@@ -742,6 +741,36 @@ def test_read_into_out_over_end_with_fill_should_return_full_data_and_write_into
     assert out.shape == (4, sf_stereo_r.channels)
 
 
+def test_read_into_out_with_frames_and_fill_value(sf_stereo_r):
+    out = np.ones((8, sf_stereo_r.channels), dtype='float64')
+    data = sf_stereo_r.read(3, out=out, fill_value=0)
+    assert len(data) == 3
+    assert np.all(data == data_stereo[:3])
+    assert np.all(data == out[:3])
+    assert data.base is out
+    assert np.all(out[3:] == 1)
+
+
+def test_read_into_out_over_end_with_frames_and_fill_value(sf_stereo_r):
+    out = np.ones((8, sf_stereo_r.channels), dtype='float64')
+    data = sf_stereo_r.read(6, out=out, fill_value=0)
+    assert len(data) == 6
+    assert np.all(out[:4] == data_stereo)
+    assert np.all(out[4:6] == 0)
+    assert np.all(out[6:8] == 1)
+    assert np.all(data == out[:6])
+    assert data.base is out
+
+
+def test_read_into_out_over_end_with_too_large_frames_and_fill_value(sf_stereo_r):
+    out = np.ones((8, sf_stereo_r.channels), dtype='float64')
+    data = sf_stereo_r.read(99, out=out, fill_value=0)
+    assert len(data) == 8
+    assert np.all(out[:4] == data_stereo)
+    assert np.all(out[4:8] == 0)
+    assert data is out
+
+
 # -----------------------------------------------------------------------------
 # Test buffer read
 # -----------------------------------------------------------------------------