Assign random plot colors for bands that don't have preassigned colors

avocado/astronomical_object.py

@@ -7,7 +7,7 @@
 import pandas as pd
 from scipy.optimize import minimize
 
-from .instruments import band_central_wavelengths, band_plot_colors
+from .instruments import band_central_wavelengths, get_band_plot_color
 from .utils import logger
 
 class AstronomicalObject():
@@ -368,7 +368,7 @@ def plot_light_curve(self, show_gp=True, verbose=False, axis=None,
         for band_idx, band in enumerate(self.bands):
             mask = observations['band'] == band
             band_data = observations[mask]
-            color = band_plot_colors[band]
+            color = get_band_plot_color(band)
 
             axis.errorbar(band_data['time'], band_data['flux'],
                           band_data['flux_error'], fmt='o', c=color,

avocado/instruments.py

@@ -22,3 +22,31 @@
     'lsstz': 'C3',
     'lssty': 'goldenrod',
 }
+
+def get_band_plot_color(band):
+    """Return the plot color for a given band.
+
+    If the band does not yet have a color assigned to it, then a random color
+    will be assigned (in a systematic way).
+
+    Parameters
+    ----------
+    band : str
+        The name of the band to use.
+    """
+    if band in band_plot_colors:
+        return band_plot_colors[band]
+
+    print("No plot color assigned for band %s, assigning a random one." % band)
+
+    # Systematic random colors. We use the hash of the band name.
+    # Note: hash() uses a random offset in python 3 so it isn't consistent
+    # between runs!
+    import hashlib
+    hasher = hashlib.md5()
+    hasher.update(band.encode('utf8'))
+    hex_color = '#%s' % hasher.hexdigest()[-6:]
+
+    band_plot_colors[band] = hex_color
+
+    return hex_color