import xarray in Velocity, remove dependecy

Author: stephaniegott

ipyleaflet/leaflet.py

@@ -329,6 +329,15 @@ class VideoOverlay(RasterLayer):
 
 
 class Velocity(Layer):
+    try:
+        import xarray
+    except ModuleNotFoundError:
+        raise ImportError(
+            'The `xarray` module (required for use of the Velocity layer) is'
+            'not installed. Run "$ pip install xarray" to install the latest'
+            'version.'
+        )
+
     _view_name = Unicode('LeafletVelocityView').tag(sync=True)
     _model_name = Unicode('LeafletVelocityModel').tag(sync=True)
 

setup.py

@@ -137,8 +137,7 @@ def run(self):
     'install_requires': [
         'ipywidgets>=7.5.0,<8',
         'traittypes>=0.2.1,<3',
-        'xarray>=0.10',
-        'branca>=0.3.1,<0.4'
+        'branca>=0.3.1,<0.4',
     ],
     'packages': find_packages(),
     'zip_safe': False,