Merge pull request #1857 from meeseeksmachine/auto-backport-of-pr-185…

…0-on-v3.1.x

Backport PR #1850 on branch v3.1.x (layer-lettering to handle 2 "digits" (up to 700 layers))

CHANGES.rst

@@ -11,6 +11,8 @@ Bug Fixes
 - Prevent duplicate labels by changing duplicate number appended
   to label to max number (of duplicates) plus 1. [#1824]
 
+- Layer lettering now supports up to 702 layers. Beyond that, special characters are used. [#1850]
+
 Cubeviz
 ^^^^^^^
 

jdaviz/app.py

@@ -47,7 +47,7 @@
 from jdaviz.core.registries import (tool_registry, tray_registry, viewer_registry,
                                     data_parser_registry)
 from jdaviz.core.tools import ICON_DIR
-from jdaviz.utils import SnackbarQueue, ColorCycler
+from jdaviz.utils import SnackbarQueue, ColorCycler, alpha_index
 from ipypopout import PopoutButton
 
 __all__ = ['Application']
@@ -380,7 +380,7 @@ def _on_layers_changed(self, msg):
 
         if layer_name not in self.state.layer_icons:
             self.state.layer_icons = {**self.state.layer_icons,
-                                      layer_name: chr(97 + len(self.state.layer_icons))}
+                                      layer_name: alpha_index(len(self.state.layer_icons))}
 
     def _link_new_data(self, reference_data=None, data_to_be_linked=None):
         """

jdaviz/tests/test_utils.py

@@ -0,0 +1,16 @@
+import pytest
+
+from jdaviz import utils
+
+
+@pytest.mark.parametrize("test_input,expected", [(0, 'a'), (1, 'b'), (25, 'z'), (26, 'aa'),
+                                                 (701, 'zz'), (702, '{a')])
+def test_alpha_index(test_input, expected):
+    assert utils.alpha_index(test_input) == expected
+
+
+def test_alpha_index_exceptions():
+    with pytest.raises(TypeError, match="index must be an integer"):
+        utils.alpha_index(4.2)
+    with pytest.raises(ValueError, match="index must be positive"):
+        utils.alpha_index(-1)

jdaviz/utils.py

@@ -10,7 +10,7 @@
 from glue.config import settings
 
 __all__ = ['SnackbarQueue', 'enable_hot_reloading', 'bqplot_clear_figure',
-           'standardize_metadata', 'ColorCycler']
+           'standardize_metadata', 'ColorCycler', 'alpha_index']
 
 # For Metadata Viewer plugin internal use only.
 PRIHDR_KEY = '_primary_header'
@@ -175,6 +175,42 @@ def bqplot_clear_figure(fig):
     setattr(fig, 'axis_registry', {})
 
 
+def alpha_index(index):
+    """Converts an index to label (A-Z, AA-ZZ).
+
+    Parameters
+    ----------
+    index : int
+        Index between 0 and 701, inclusive. Higher number is accepted but
+        will have special characters.
+
+    Returns
+    -------
+    label : str
+        String in the range A-Z, AA-ZZ if index is within 0-701 range, inclusive.
+
+    Raises
+    ------
+    TypeError
+        Index is not integer.
+
+    ValueError
+        Index is negative.
+    """
+    # if we ever want to support more than 702 layers, then we'll need a third
+    # "digit" and will need to account for the horizontal space in the legends
+    if not isinstance(index, int):
+        raise TypeError("index must be an integer")
+    if index < 0:
+        raise ValueError("index must be positive")
+    if index <= 25:
+        # a-z
+        return chr(97 + index)
+    else:
+        # aa-zz (26-701), then overflow strings like '{a'
+        return chr(97 + index//26 - 1) + chr(97 + index % 26)
+
+
 def standardize_metadata(metadata):
     """Standardize given metadata so it can be viewed in
     Metadata Viewer plugin. The input can be plain