From f63ad3bfbc5ab7cecf00f4b012d18253e9c5e733 Mon Sep 17 00:00:00 2001
From: Julien Seguinot <1186928+juseg@users.noreply.github.com>
Date: Tue, 11 Jun 2024 11:33:58 +0200
Subject: [PATCH 1/2] Add accessor method cf.assign().

---
 cf_xarray/accessor.py | 48 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index a10c4886..34583611 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -2633,6 +2633,54 @@ def grid_mapping_names(self) -> dict[str, list[str]]:
                 results[v].append(k)
         return results
 
+    def assign(self, **standard_variables: Any) -> Dataset:
+        """Assign new variables by standard_name.
+
+        Parameters
+        ----------
+        standard_variables : mapping
+            A mapping from netCDF Climate and Forecast compliant standard names
+            (http://cfconventions.org/standard-names.html), to the new values.
+            The new values are passed to ``:meth:Dataset.assign``.
+
+        Returns
+        -------
+        dataset : Dataset
+            A new dataset with the new variables added, replacing any existing
+            variable with the same standard name. New variables are labelled
+            according to their input (short) names, or standard names if short
+            names are missing, with added trailing underscores in the event of
+            duplicates.
+
+        See Also
+        --------
+        DataSet.assign
+        """
+
+        # initalize dictionary mapping short names to the new variables
+        variables = {}
+
+        # for each standard name and value pair
+        for standard_name, values in standard_variables.items():
+
+            # default to using existing short name or standard name
+            name = getattr(values, "name", standard_name)
+
+            # add trailing underscores until we find a free slot
+            while name in self._obj.data_vars or name in variables:
+                emit_user_level_warning(
+                    f"found existing variable {name}, using {name}_ instead",
+                    UserWarning)
+                name += '_'
+
+            # map name to values (without coords, see #513, xarray#6447)
+            values = xr.as_variable(values)
+            values.attrs.update(standard_name=standard_name)
+            variables[name] = values
+
+        # assign new variables and return a new dataset
+        return self._obj.assign(variables)
+
     def decode_vertical_coords(self, *, outnames=None, prefix=None):
         """
         Decode parameterized vertical coordinates in place.

From 2a54d922259c8d1a6694f3958ba1ccbe9c2122c1 Mon Sep 17 00:00:00 2001
From: "pre-commit-ci[bot]"
 <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Date: Tue, 11 Jun 2024 11:53:45 +0000
Subject: [PATCH 2/2] [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci
---
 cf_xarray/accessor.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/cf_xarray/accessor.py b/cf_xarray/accessor.py
index 34583611..1795b726 100644
--- a/cf_xarray/accessor.py
+++ b/cf_xarray/accessor.py
@@ -2662,7 +2662,6 @@ def assign(self, **standard_variables: Any) -> Dataset:
 
         # for each standard name and value pair
         for standard_name, values in standard_variables.items():
-
             # default to using existing short name or standard name
             name = getattr(values, "name", standard_name)
 
@@ -2670,8 +2669,9 @@ def assign(self, **standard_variables: Any) -> Dataset:
             while name in self._obj.data_vars or name in variables:
                 emit_user_level_warning(
                     f"found existing variable {name}, using {name}_ instead",
-                    UserWarning)
-                name += '_'
+                    UserWarning,
+                )
+                name += "_"
 
             # map name to values (without coords, see #513, xarray#6447)
             values = xr.as_variable(values)