Simplify NDCube.to_nddata

changelog/892.feature.rst

@@ -0,0 +1 @@
+`~ndcube.NDCube` now accepts ``global_coords=`` and ``extra_coords=`` in the constructor of the class.

ndcube/ndcube.py

@@ -48,8 +48,6 @@
 except ImportError:
     pass
 
-COPY = object()
-
 
 class NDCubeABC(astropy.nddata.NDDataBase):
 
@@ -381,25 +379,27 @@ class NDCubeBase(NDCubeABC, astropy.nddata.NDData, NDCubeSlicingMixin):
     _global_coords = NDCubeLinkedDescriptor(GlobalCoords)
 
     def __init__(self, data, wcs=None, uncertainty=None, mask=None, meta=None,
-                 unit=None, copy=False, **kwargs):
+                 unit=None, copy=False, psf=None, *, extra_coords=None, global_coords=None, **kwargs):
 
         super().__init__(data, wcs=wcs, uncertainty=uncertainty, mask=mask,
-                         meta=meta, unit=unit, copy=copy, **kwargs)
+                         meta=meta, unit=unit, copy=copy, psf=psf, **kwargs)
 
         # Enforce that the WCS object is not None
         if self.wcs is None:
             raise TypeError("The WCS argument can not be None.")
 
         # Get existing extra_coords if initializing from an NDCube
-        if hasattr(data, "extra_coords"):
+        if extra_coords is None and getattr(data, "extra_coords", None) is not None:
             extra_coords = data.extra_coords
+        if extra_coords is not None:
             if copy:
                 extra_coords = deepcopy(extra_coords)
             self._extra_coords = extra_coords
 
         # Get existing global_coords if initializing from an NDCube
-        if hasattr(data, "global_coords"):
+        if global_coords is None and getattr(data, "global_coords", None) is not None:
             global_coords = data._global_coords
+        if global_coords is not None:
             if copy:
                 global_coords = deepcopy(global_coords)
             self._global_coords = global_coords
@@ -1465,24 +1465,28 @@ def fill_masked(self, fill_value, uncertainty_fill_value=None, unmask=False, fil
 
     def to_nddata(self,
                   *,
-                  data=COPY,
-                  wcs=COPY,
-                  uncertainty=COPY,
-                  mask=COPY,
-                  unit=COPY,
-                  meta=COPY,
-                  psf=COPY,
-                  extra_coords=COPY,
-                  global_coords=COPY,
+                  data="copy",
+                  wcs="copy",
+                  uncertainty="copy",
+                  mask="copy",
+                  unit="copy",
+                  meta="copy",
+                  psf="copy",
                   nddata_type=NDData,
                   **kwargs,
                  ):
         """
-        Constructs new type instance with the same attribute values as this `~ndcube.NDCube`.
-
-        Attribute values can be altered on the output object by setting a kwarg with the new
-        value, e.g. ``data=new_data``.
-        Any attributes not supported by the new class (``nddata_type``), will be discarded.
+        Constructs a new `~astropy.nddata.NDData` instance from this object.
+
+        By default all known ``NDData`` attributes are copied (by reference) from
+        this object, values can be altered on the output object by
+        setting a kwarg with the new value, e.g. ``data=new_data``.
+        Custom attributes on this class can be passed by setting that
+        keyword to `"copy"`, for example ``mycube.to_nddata(spam="copy")``
+        is the equivalent of setting
+        ``mycube.to_nddata(spam=mycube.spam)``.
+        Any attributes not supported by the new class
+        (``nddata_type``), will be discarded.
 
         Parameters
         ----------
@@ -1500,20 +1504,16 @@ def to_nddata(self,
             Metadata object of new instance. Default is to use data of this instance.
         psf: Any, optional
             PSF object of new instance. Default is to use data of this instance.
-        extra_coords: `ndcube.ExtraCoordsABC`, optional
-            Extra coords object of new instance. Default is to use data of this instance.
-        global_coords: `ndcube.GlobalCoordsABC`, optional
-            WCS object of new instance. Default is to use data of this instance.
         nddata_type: Any, optional
             The type of the returned object. Must be a subclass of `~astropy.nddata.NDData`
             or a class that behaves like one.  Default=`~astropy.nddata.NDData`.
         kwargs:
-            Additional inputs to the ``nddata_type`` constructor that should differ from,
-            or are not represented by, the  attributes of this instance. For example, to
+            Additional inputs to the ``nddata_type`` constructor. For example, to
             set different data values on the returned object, set a kwarg ``data=new_data``,
-            where ``new_data`` is an array of compatible shape and dtype. Note that kwargs
-            given by the user and attributes on this instance that are not supported by the
-            ``nddata_type`` constructor are ignored.
+            where ``new_data`` is an array of compatible shape and dtype.
+            Other keyword arguments can be specified to copy custom
+            attributes with the value ``"copy"``, for example
+            ``global_coords="copy"``.
 
         Returns
         -------
@@ -1525,39 +1525,31 @@ def to_nddata(self,
         Examples
         --------
         To create an `~astropy.nddata.NDData` instance which is a copy of an `~ndcube.NDCube`
-        (called ``cube``) without a WCS, do:
+        (called ``cube``) without a WCS, do::
 
         >>> nddata_without_coords = cube.to_nddata(wcs=None) # doctest: +SKIP
+
+        To create a new `~ndcube.NDCube` instance which is a copy of
+        an `~ndcube.NDCube` (called ``cube``) without an uncertainty,
+        but with ``global_coords`` and ``extra_coords`` do::
+
+        >>> nddata_without_coords = cube.to_nddata(uncertainty=None, global_coords=True, extra_coords=True) # doctest: +SKIP
         """
-        # Build dictionary of new attribute values from this NDCube instance
-        # and update with user-defined kwargs. Remove any kwargs not set by user.
+        # Put all NDData kwargs in a dict
         user_kwargs = {"data": data,
                        "wcs": wcs,
                        "uncertainty": uncertainty,
                        "mask": mask,
                        "unit": unit,
                        "meta": meta,
                        "psf": psf,
-                       "extra_coords": extra_coords,
-                       "global_coords": global_coords}
-        user_kwargs = {key: value for key, value in user_kwargs.items() if value is not COPY}
-        user_kwargs.update(kwargs)
-        all_kwargs = {key.strip("_"): value for key, value in self.__dict__.items()}
-        all_kwargs.update(user_kwargs)
-        # Inspect call signature of new_nddata class and
-        # remove unsupported items from new_kwargs.
-        all_kwargs = {key: value for key, value in all_kwargs.items()
-                      if key in inspect.signature(nddata_type).parameters.keys()}
+                       **kwargs}
+        # If any are "copy" then copy by reference
+        user_kwargs = {key: getattr(self, key)
+                       if isinstance(value, str) and value == "copy" else value
+                       for key, value in user_kwargs.items()}
         # Construct and return new instance.
-        new_nddata = nddata_type(**all_kwargs)
-        if isinstance(new_nddata, NDCubeBase):
-            if extra_coords is COPY:
-                extra_coords = copy.copy(self._extra_coords)
-                extra_coords._ndcube = new_nddata
-                new_nddata._extra_coords = extra_coords
-            if global_coords is COPY:
-                new_nddata._global_coords = copy.copy(self._global_coords)
-        return new_nddata
+        return nddata_type(**user_kwargs)
 
 
 def _create_masked_array_for_rebinning(data, mask, operation_ignores_mask):

ndcube/tests/test_ndcube.py

@@ -44,6 +44,24 @@ def test_initialize_from_ndcube(ndcube_3d_l_ln_lt_ectime):
     assert ec is not ec3
 
 
+def test_initialize_with_extra_global_coords(ndcube_3d_ln_lt_l_ec_all_axes):
+    ndc = ndcube_3d_ln_lt_l_ec_all_axes[:, :, 0]
+    data = ndc.data
+    wcs = ndc.wcs
+    ec = ndc.extra_coords
+    gc = ndc.global_coords
+
+    new_cube = NDCube(data, wcs=wcs, extra_coords=ec, global_coords=gc)
+    assert new_cube.extra_coords is ec
+    assert new_cube.global_coords is gc
+
+    new_cube_copy = NDCube(data, wcs=wcs, extra_coords=ec, global_coords=gc, copy=True)
+    assert new_cube_copy.extra_coords is not ec
+    assert new_cube_copy.global_coords is not gc
+    helpers.assert_extra_coords_equal(new_cube_copy.extra_coords, ec)
+    helpers.assert_global_coords_equal(new_cube_copy.global_coords, gc)
+
+
 def test_wcs_type_after_init(ndcube_3d_ln_lt_l, wcs_3d_l_lt_ln):
     # Generate a low level WCS
     slices = np.s_[:, :, 0]
@@ -254,8 +272,23 @@ def test_to_nddata_type_ndcube(ndcube_2d_ln_lt_uncert_ec):
     ndc = ndcube_2d_ln_lt_uncert_ec
     ndc.global_coords.add("wavelength", "em.wl", 100*u.nm)
     new_data = ndc.data * 2
-    output = ndc.to_nddata(data=new_data, nddata_type=NDCube)
+    output = ndc.to_nddata(data=new_data, extra_coords="copy", global_coords="copy", nddata_type=NDCube)
     assert type(output) is NDCube
     assert (output.data == new_data).all()
     helpers.assert_extra_coords_equal(output.extra_coords, ndc.extra_coords)
     helpers.assert_global_coords_equal(output.global_coords, ndc.global_coords)
+
+
+def test_custom_tonddata_type(ndcube_2d_ln_lt):
+    ndc = ndcube_2d_ln_lt
+    ndc.spam = "Eggs"
+
+    class MyNDData(astropy.nddata.NDData):
+        def __init__(self, data, *, spam=None, **kwargs):
+            super().__init__(data, **kwargs)
+            self.spam = spam
+
+    new_ndd = ndc.to_nddata(spam="copy", nddata_type=MyNDData)
+    assert new_ndd.spam == "Eggs"
+    assert new_ndd.data is ndc.data
+    assert new_ndd.wcs is ndc.wcs