build: make xesmf optional dependency

pyproject.toml

@@ -53,7 +53,6 @@ dependencies = [
   "deprecation",
   "pooch",
   "scikit-learn",
-  "xesmf",
 ###
 # optimization
 ###
@@ -79,6 +78,9 @@ dependencies = [
 ]
 
 [project.optional-dependencies]
+synth = [
+  "xesmf",
+]
 test = [
   "pytest >=6",
   "pytest-cov >=3",
@@ -97,7 +99,7 @@ docs = [
   "sphinxcontrib-bibtex",
 ]
 dev = [
-  "invert4geom[test,docs]",
+  "invert4geom[test,docs, synth]",
   "ruff",
   "nox",
   "pre-commit",
@@ -108,7 +110,7 @@ dev = [
   "mypy",
 ]
 all = [
-  "invert4geom[test,dev,docs]",
+  "invert4geom[test,dev,docs,synth]",
 ]
 
 [project.urls]

src/invert4geom/synthetic.py

@@ -9,13 +9,17 @@
 import pooch
 import verde as vd
 import xarray as xr
-import xesmf
 from numpy.typing import NDArray
 from polartoolkit import fetch, maps
 from polartoolkit import utils as polar_utils
 
 from invert4geom import cross_validation, log, utils
 
+try:
+    import xesmf
+except ImportError:
+    xesmf = None
+
 
 def load_synthetic_model(
     spacing: float = 1e3,
@@ -283,6 +287,12 @@ def contaminate_with_long_wavelength_noise(
     xarray.DataArray
         Contaminated grid
     """
+    if xesmf is None:
+        msg = (
+            "To use the `contaminate_with_long_wavelength_noise` function, you must "
+            "have the `xesmf` package installed."
+        )
+        raise ImportError(msg)
 
     grid = copy.deepcopy(grid)
 
@@ -310,6 +320,7 @@ def contaminate_with_long_wavelength_noise(
         data=None,
         data_names=None,
     ).rename({"northing": "lat", "easting": "lon"})
+
     low_res_grid = xesmf.Regridder(
         grid.rename({"northing": "lat", "easting": "lon"}),
         low_res_grid,