BF+TST - test calc scale force and add reset

Think a bit more about caching of slope, inter and finite_range.  Add
tests for recalculation of slope, scale. Add reset method and test.

Author: matthew-brett

nibabel/arraywriters.py

@@ -66,6 +66,7 @@ def __init__(self, array, out_dtype=None, calc_scale=True):
         else:
             out_dtype = np.dtype(out_dtype)
         self._out_dtype = out_dtype
+        self._finite_range = None
         if self.scaling_needed():
             raise WriterError("Scaling needed but cannot scale")
 
@@ -138,11 +139,8 @@ def out_dtype(self):
 
     def finite_range(self):
         """ Return (maybe cached) finite range of data array """
-        try:
-            return self._finite_range
-        except AttributeError:
-            pass
-        self._finite_range = finite_range(self._array)
+        if self._finite_range is None:
+            self._finite_range = finite_range(self._array)
         return self._finite_range
 
     def _writing_range(self):
@@ -223,13 +221,17 @@ def __init__(self, array, out_dtype=None, calc_scale=True,
         else:
             out_dtype = np.dtype(out_dtype)
         self._out_dtype = out_dtype
-        self.needs_scale = self.scaling_needed()
         self.scaler_dtype = np.dtype(scaler_dtype)
-        self.slope = 1.0
-        self._scale_calced = False
+        self.reset()
         if calc_scale:
             self.calc_scale()
 
+    def reset(self):
+        """ Set object to values before any scaling calculation """
+        self.slope = 1.0
+        self._finite_range = None
+        self._scale_calced = False
+
     def _get_slope(self):
         return self._slope
     def _set_slope(self, val):
@@ -242,10 +244,11 @@ def calc_scale(self, force=False):
         # If we've run already, return unless told otherwise
         if not force and self._scale_calced:
             return
-        self._scale_calced = True
+        self.reset()
         if not self.scaling_needed():
             return
         self._do_scaling()
+        self._scale_calced = True
 
     def to_fileobj(self, fileobj, order='F', nan2zero=True):
         """ Write array into `fileobj`
@@ -361,11 +364,15 @@ def __init__(self, array, out_dtype=None, calc_scale=True,
         >>> (aw.slope, aw.inter) == (1.0, 128)
         True
         """
-        super(SlopeInterArrayWriter, self).__init__(array, out_dtype, False,
+        super(SlopeInterArrayWriter, self).__init__(array,
+                                                    out_dtype,
+                                                    calc_scale,
                                                     scaler_dtype)
+
+    def reset(self):
+        """ Set object to values before any scaling calculation """
+        super(SlopeInterArrayWriter, self).reset()
         self.inter = 0.0
-        if calc_scale:
-            self.calc_scale()
 
     def _get_inter(self):
         return self._inter

nibabel/tests/test_arraywriters.py

@@ -268,7 +268,31 @@ def test_calculate_scale():
     assert_raises(WriterError, SAW, npa([-1, 1], dtype=np.int8), np.uint8)
     # Offset trick can't work when max is out of range
     aw = SIAW(npa([-1, 255], dtype=np.int16), np.uint8)
-    assert_not_equal(get_slope_inter(aw), (1.0, -1.0))
+    slope_inter = get_slope_inter(aw)
+    assert_not_equal(slope_inter, (1.0, -1.0))
+
+
+def test_resets():
+    # Test reset of values, caching of scales
+    for klass, inp, outp in ((SlopeInterArrayWriter, (1, 511), (2.0, 1.0)),
+                             (SlopeArrayWriter, (0, 510), (2.0, 0.0))):
+        arr = np.array(inp)
+        outp = np.array(outp)
+        aw = klass(arr, np.uint8)
+        assert_array_equal(get_slope_inter(aw), outp)
+        aw.calc_scale() # cached no change
+        assert_array_equal(get_slope_inter(aw), outp)
+        aw.calc_scale(force=True) # same data, no change
+        assert_array_equal(get_slope_inter(aw), outp)
+        # Change underlying array
+        aw.array[:] = aw.array * 2
+        aw.calc_scale() # cached still
+        assert_array_equal(get_slope_inter(aw), outp)
+        aw.calc_scale(force=True) # new data, change
+        assert_array_equal(get_slope_inter(aw), outp * 2)
+        # Test reset
+        aw.reset()
+        assert_array_equal(get_slope_inter(aw), (1.0, 0.0))
 
 
 def test_no_offset_scale():