FIELDSETS: allow merge function to accept a single argument [MPY-310]

Author: iainrussell

metview/bindings.py

@@ -1016,6 +1016,7 @@ def bind_functions(namespace, module_name=None):
     namespace["setoutput"] = setoutput
     namespace["metzoom"] = metzoom
     namespace["version_info"] = version_info
+    namespace["merge"] = merge
     namespace["dataset_to_fieldset"] = dataset_to_fieldset
 
     namespace["Fieldset"] = Fieldset
@@ -1034,7 +1035,7 @@ def bind_functions(namespace, module_name=None):
 greater_than = make(">")
 lower_equal_than = make("<=")
 lower_than = make("<")
-merge = make("&")
+met_merge = make("&")
 met_not_eq = make("<>")
 met_plot = make("plot")
 mod = make("mod")
@@ -1063,6 +1064,14 @@ def version_info():
     return binary_info
 
 
+# wrapper so that we can merge a single value (just returns itself)
+def merge(*args):
+    if len(args) == 1:
+        return args[0]
+    else:
+        return met_merge(*args)
+
+
 # -----------------------------------------------------------------------------
 #                        Particular code for calling the plot() command
 # -----------------------------------------------------------------------------

tests/test_metview.py

@@ -822,6 +822,34 @@ def test_fieldset_create_from_list_of_fieldsets_5():
         gl = mv.Fieldset(path=os.path.join(PATH, "test.grib"), fields=list_of_fields)
 
 
+def test_fieldset_merge_1():
+    grib = mv.read(os.path.join(PATH, "t_for_xs.grib"))
+    g3 = mv.merge(grib[1], grib[0])
+    assert g3.count() == 2
+    assert g3.grib_get_long("level") == [850, 1000]
+
+
+def test_fieldset_merge_2():
+    grib = mv.read(os.path.join(PATH, "t_for_xs.grib"))
+    g3 = mv.merge(grib[1], grib[0], grib[4])
+    assert g3.count() == 3
+    assert g3.grib_get_long("level") == [850, 1000, 400]
+
+
+def test_fieldset_merge_3():
+    grib = mv.read(os.path.join(PATH, "t_for_xs.grib"))
+    g3 = mv.merge(grib[2])
+    assert g3.count() == 1
+    assert g3.grib_get_long("level") == 700
+
+
+def test_fieldset_merge_4():
+    grib = mv.read(os.path.join(PATH, "t_for_xs.grib"))
+    g3 = mv.merge(grib[:3])
+    assert g3.count() == 3
+    assert g3.grib_get_long("level") == [1000, 850, 700]
+
+
 def test_fieldset_pickling():
     pickled_fname = file_in_testdir("pickled_fieldset.p")
     g = mv.Fieldset(path=os.path.join(PATH, "tuv_pl.grib"))