Make mhealpy an optional import

companion.txt

@@ -3,7 +3,6 @@ gwpy>=0.8.1
 
 # HEALPix is very useful for some analysis.
 healpy
-mhealpy
 
 # Needed for GraceDB uploads and skymap generation
 ligo-gracedb>=2.10.0

pycbc/distributions/sky_location.py

@@ -22,12 +22,15 @@
 
 
 from scipy.spatial.transform import Rotation
-from mhealpy import HealpixMap
 
 from pycbc.distributions import angular
 from pycbc import VARARGS_DELIM
 from pycbc.io import FieldArray
 from pycbc.types import angle_as_radians
+from pycbc.libutils import import_optional
+
+mhealpy = import_optional('mhealpy')
+
 
 logger = logging.getLogger('pycbc.distributions.sky_location')
 
@@ -182,7 +185,7 @@ class HealpixSky:
     def __init__(self, **params):
         # Read the map file.
         file_name = params['healpix_file']
-        self.healpix_map = HealpixMap.read_map(file_name)
+        self.healpix_map = mhealpy.HealpixMap.read_map(file_name)
 
         # Get the probabilities at each pixel.
         if self.healpix_map.density():