Move interface definition from base class to protocol

astrowidgets/__init__.py

@@ -6,4 +6,4 @@
 from ._astropy_init import *  # noqa
 # ----------------------------------------------------------------------------
 
-from .core import *  # noqa
+from .ginga import *  # noqa

astrowidgets/core.py → astrowidgets/ginga.py

@@ -23,12 +23,6 @@
 
 __all__ = ['ImageWidget']
 
-# Allowed locations for cursor display
-ALLOWED_CURSOR_LOCATIONS = ['top', 'bottom', None]
-
-# List of marker names that are for internal use only
-RESERVED_MARKER_SET_NAMES = ['all']
-
 
 class ImageWidget(ipyw.VBox):
     """
@@ -55,6 +49,11 @@ class ImageWidget(ipyw.VBox):
         correct value to use.*
 
     """
+    # Allowed locations for cursor display
+    ALLOWED_CURSOR_LOCATIONS = ('top', 'bottom', None)
+
+    # List of marker names that are for internal use only
+    RESERVED_MARKER_SET_NAMES = ('all', )
 
     def __init__(self, logger=None, image_width=500, image_height=500,
                  pixel_coords_offset=0, **kwargs):
@@ -565,6 +564,9 @@ def get_markers(self, x_colname='x', y_colname='y',
                     del table[skycoord_colname]
                 tables.append(table)
 
+            if len(tables) == 0:
+                return None
+
             stacked = vstack(tables, join_type='exact')
 
             if coordinates:
@@ -648,11 +650,11 @@ def _validate_marker_name(self, marker_name):
         """
         Raise an error if the marker_name is not allowed.
         """
-        if marker_name in RESERVED_MARKER_SET_NAMES:
+        if marker_name in self.RESERVED_MARKER_SET_NAMES:
             raise ValueError('The marker name {} is not allowed. Any name is '
                              'allowed except these: '
                              '{}'.format(marker_name,
-                                         ', '.join(RESERVED_MARKER_SET_NAMES)))
+                                         ', '.join(self.RESERVED_MARKER_SET_NAMES)))
 
     def add_markers(self, table, x_colname='x', y_colname='y',
                     skycoord_colname='coord', use_skycoord=False,
@@ -888,7 +890,7 @@ def cursor(self, val):
         else:
             raise ValueError('Invalid value {} for cursor.'
                              'Valid values are: '
-                             '{}'.format(val, ALLOWED_CURSOR_LOCATIONS))
+                             '{}'.format(val, self.ALLOWED_CURSOR_LOCATIONS))
         self._cursor = val
 
     @property

astrowidgets/interface_definition.py

@@ -0,0 +1,111 @@
+from typing import Protocol, runtime_checkable, Any
+from abc import abstractmethod
+
+# Allowed locations for cursor display
+ALLOWED_CURSOR_LOCATIONS = ['top', 'bottom', None]
+
+# List of marker names that are for internal use only
+RESERVED_MARKER_SET_NAMES = ['all']
+
+__all__ = [
+    'ImageViewerInterface',
+    'ALLOWED_CURSOR_LOCATIONS',
+    'RESERVED_MARKER_SET_NAMES'
+]
+
+
+@runtime_checkable
+class ImageViewerInterface(Protocol):
+    # This are attributes, not methods. The type annotations are there
+    # to make sure Protocol knows they are attributes. Python does not
+    # do any checking at all of these types.
+    click_center: bool
+    click_drag: bool
+    scroll_pan: bool
+    image_width: int
+    image_height: int
+    zoom_level: float
+    marker: Any
+    cuts: Any
+    stretch: str
+    # viewer: Any
+
+    # Allowed locations for cursor display
+    ALLOWED_CURSOR_LOCATIONS = ('top', 'bottom', None)
+
+    # List of marker names that are for internal use only
+    RESERVED_MARKER_SET_NAMES = ('all', )
+
+    # The methods, grouped loosely by purpose
+
+    # Methods for loading data
+    @abstractmethod
+    def load_fits(self, file):
+        raise NotImplementedError
+
+    @abstractmethod
+    def load_array(self, array):
+        raise NotImplementedError
+
+    @abstractmethod
+    def load_nddata(self, data):
+        raise NotImplementedError
+
+    # Saving contents of the view and accessing the view
+    @abstractmethod
+    def save(self, filename):
+        raise NotImplementedError
+
+    # Marker-related methods
+    @abstractmethod
+    def start_marking(self, marker_name=None):
+        raise NotImplementedError
+
+    @abstractmethod
+    def stop_marking(self, clear_markers=False):
+        raise NotImplementedError
+
+    @abstractmethod
+    def add_markers(self, table, x_colname='x', y_colname='y',
+                    skycoord_colname='coord', use_skycoord=False,
+                    marker_name=None):
+        raise NotImplementedError
+
+    # @abstractmethod
+    # def remove_all_markers(self):
+    #     raise NotImplementedError
+
+    @abstractmethod
+    def reset_markers(self):
+        raise NotImplementedError
+
+    # @abstractmethod
+    # def remove_markers_by_name(self, marker_name=None):
+    #     raise NotImplementedError
+
+    @abstractmethod
+    def remove_markers(self, marker_name=None):
+        raise NotImplementedError
+
+    # @abstractmethod
+    # def get_all_markers(self):
+    #     raise NotImplementedError
+
+    @abstractmethod
+    def get_markers(self, x_colname='x', y_colname='y',
+                    skycoord_colname='coord',
+                    marker_name=None):
+        raise NotImplementedError
+
+    # Methods that modify the view
+    @abstractmethod
+    def center_on(self):
+        raise NotImplementedError
+
+    @abstractmethod
+    def offset_by(self):
+        raise NotImplementedError
+
+    @abstractmethod
+    def zoom(self):
+        raise NotImplementedError