Netcdf is an optional dependency

pysteps/blending/utils.py

@@ -21,12 +21,19 @@
 from pathlib import Path
 
 import numpy as np
-import netCDF4
 
 from pysteps.cascade import get_method as cascade_get_method
 from pysteps.cascade.bandpass_filters import filter_gaussian
+from pysteps.exceptions import MissingOptionalDependency
 from pysteps.utils import get_method as utils_get_method
 
+try:
+    import netCDF4
+
+    NETCDF4_IMPORTED = True
+except ImportError:
+    NETCDF4_IMPORTED = False
+
 
 def stack_cascades(R_d, donorm=True):
     """Stack the given cascades into a larger array.
@@ -298,9 +305,15 @@ def decompose_NWP(
 
     Returns
     -------
-    Nothing
+    None
     """
 
+    if not NETCDF4_IMPORTED:
+        raise MissingOptionalDependency(
+            "netCDF4 package is required to save the decomposed NWP data, "
+            "but it is not installed"
+        )
+
     # Make a NetCDF file
     output_date = f"{analysis_time.astype(datetime.datetime):%Y%m%d%H%M%S}"
     outfn = Path(output_path) / f"cascade_{NWP_model}_{output_date}.nc"
@@ -443,6 +456,12 @@ def load_NWP(input_nc_path_decomp, input_path_velocities, start_time, n_timestep
       of the advection field for the (NWP) model field per forecast lead time.
     """
 
+    if not NETCDF4_IMPORTED:
+        raise MissingOptionalDependency(
+            "netCDF4 package is required to load the decomposed NWP data, "
+            "but it is not installed"
+        )
+
     # Open the file
     ncf_decomp = netCDF4.Dataset(input_nc_path_decomp, "r", format="NETCDF4")
     velocities = np.load(input_path_velocities)