From a869dc7724174ef5725ae84caea92d307a739694 Mon Sep 17 00:00:00 2001
From: veenstrajelmer <60435591+veenstrajelmer@users.noreply.github.com>
Date: Fri, 16 Aug 2024 20:31:50 +0200
Subject: [PATCH] properly adding attrs after applying conversion from
 conversion_dict (#965)

* properly adding attrs after applying conversion from conversion_dict

* updated whatsnew

* improved test
---
 dfm_tools/interpolate_grid2bnd.py  | 8 +++++---
 docs/whats-new.md                  | 6 ++++++
 tests/test_interpolate_grid2bnd.py | 1 +
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/dfm_tools/interpolate_grid2bnd.py b/dfm_tools/interpolate_grid2bnd.py
index f4e03a06a..a30c8eae4 100644
--- a/dfm_tools/interpolate_grid2bnd.py
+++ b/dfm_tools/interpolate_grid2bnd.py
@@ -354,9 +354,11 @@ def ds_apply_conversion_dict(data_xr, conversion_dict, quantity):
     # TODO: maybe do unit conversion before interp or is that computationally heavy?
     if 'conversion' in conversion_dict[quantity].keys(): #if conversion is present, unit key must also be in conversion_dict
         print(f'> converting units from [{data_xr[quantity].attrs["units"]}] to [{conversion_dict[quantity]["unit"]}]')
-        #print(f'attrs are discarded:\n{data_xr_vars[quan].attrs}')
-        data_xr[quantity] = data_xr[quantity] * conversion_dict[quantity]['conversion'] #conversion drops all attributes of which units (which are changed anyway)
-        data_xr[quantity].attrs['units'] = conversion_dict[quantity]['unit'] #add unit attribute with resulting unit
+        # conversion drops all attributes of which units (which are changed anyway)
+        data_xr[quantity] = data_xr[quantity] * conversion_dict[quantity]['conversion']
+        # add unit attribute with resulting unit
+        quantity_attrs = {'units': conversion_dict[quantity]['unit']}
+        data_xr[quantity] = data_xr[quantity].assign_attrs(quantity_attrs)
     return data_xr
 
 
diff --git a/docs/whats-new.md b/docs/whats-new.md
index 7c4e91c56..bf43d8de9 100644
--- a/docs/whats-new.md
+++ b/docs/whats-new.md
@@ -1,5 +1,11 @@
 # What's new
 
+## UNRELEASED
+
+### Fix
+- properly assigning units attribute in `ds_apply_conversion_dict()` (it did not always stick) in [#965](https://github.com/Deltares/dfm_tools/pull/965)
+
+
 ## 0.25.0 (2024-08-16)
 
 ### Feat
diff --git a/tests/test_interpolate_grid2bnd.py b/tests/test_interpolate_grid2bnd.py
index 3ddfcdcf0..d9ea114b5 100644
--- a/tests/test_interpolate_grid2bnd.py
+++ b/tests/test_interpolate_grid2bnd.py
@@ -300,6 +300,7 @@ def test_ds_apply_conversion_dict_rename_and_factor():
     assert 'o2' in ds_moretime.data_vars
     assert 'tracerbndOXY' in ds_converted.data_vars
     assert np.allclose(ds_converted['tracerbndOXY'], ds_moretime['o2']*0.032, equal_nan=True)
+    assert ds_converted['tracerbndOXY'].attrs['units'] == 'g/m3'
 
 
 @pytest.mark.unittest