Unit conversion warning (#795)

* Ignoring statement for flake8

* Ignoring statement for flake8

* Adding keyword options to notify user when the unit conversion has a problem.

* Removing old unused code.

act/io/hysplit.py

@@ -78,7 +78,7 @@ def read_hysplit(filename, base_year=2000):
         for variable in data[1:]:
             var_list.append(variable)
     input_df = pd.read_csv(
-        filename, sep='\s+', index_col=False, names=var_list, skiprows=12)
+        filename, sep='\s+', index_col=False, names=var_list, skiprows=12)  # noqa W605
     input_df['year'] = base_year + input_df['year']
     input_df['time'] = pd.to_datetime(input_df[["year", "month", "day", "hour", "minute"]],
                                       format='%y%m%d%H%M')

act/utils/data_utils.py

@@ -35,7 +35,8 @@ def __init__(self, ds):
         self._ds = ds
 
     def change_units(
-        self, variables=None, desired_unit=None, skip_variables=None, skip_standard=True
+        self, variables=None, desired_unit=None, skip_variables=None, skip_standard=True,
+        verbose=False, raise_error=False
     ):
         """
         Parameters
@@ -51,6 +52,13 @@ def change_units(
             Flag indicating the QC variables that will not need changing are
             skipped. Makes the processing faster when processing all variables
             in dataset.
+        verbose : boolean
+            Option to print statement when an attempted conversion fails. Set to False
+            as default because many units strings are not udunits complient and when
+            trying to convert all varialbes of a type of units (eg temperature) the code
+            can print a lot of unecessary information.
+        raise_error : boolean
+            Raise an error if conversion is not successful.
 
         Returns
         -------
@@ -102,7 +110,11 @@ def change_units(
                 pint.errors.UndefinedUnitError,
                 np.core._exceptions.UFuncTypeError,
             ):
-                continue
+                if raise_error:
+                    raise ValueError(f"Unable to convert '{var_name}' to units of '{desired_unit}'.")
+                elif verbose:
+                    print(f"\n    Unable to convert '{var_name}' to units of '{desired_unit}'. "
+                          f"Skipping unit converstion for '{var_name}'.\n")
 
         return self._ds
 

examples/plotting/plot_scatter.py

@@ -31,7 +31,7 @@
                      'ground_speed',
                      m_field='ambient_temp',
                      marker='x',
-                     cbar_label='Ambient Temperature ($^\circ$C)'
+                     cbar_label='Ambient Temperature ($^\circ$C)'  # noqa W605
                      )
 
 # Set the range of the field on the x-axis

tests/utils/test_data_utils.py

@@ -4,6 +4,8 @@
 import pytest
 import xarray as xr
 from numpy.testing import assert_almost_equal
+from contextlib import redirect_stdout
+from io import StringIO
 
 import act
 from act.utils.data_utils import DatastreamParserARM as DatastreamParser
@@ -93,10 +95,8 @@ def test_convert_units():
     data = act.utils.data_utils.convert_units(r_data, 'K', 'C')
     assert np.ceil(data[0]) == 12
 
-    try:
+    with np.testing.assert_raises(ValueError):
         ds.utils.change_units()
-    except ValueError as error:
-        assert str(error) == "Need to provide 'desired_unit' keyword for .change_units() method"
 
     desired_unit = 'degF'
     skip_vars = [ii for ii in ds.data_vars if ii.startswith('qc_')]
@@ -138,6 +138,25 @@ def test_convert_units():
     ds.close()
     del ds
 
+    # Test if exception or print statement is issued when an error occurs with units string
+    ds = act.io.arm.read_arm_netcdf(act.tests.sample_files.EXAMPLE_EBBR1)
+    with np.testing.assert_raises(ValueError):
+        ds.utils.change_units('home_signal_15', 'not_a_real_unit_string', raise_error=True)
+
+    with np.testing.assert_raises(ValueError):
+        ds.utils.change_units('not_a_real_variable_name', 'degC', raise_error=True)
+
+    f = StringIO()
+    var_name = 'home_signal_15'
+    unit = 'not_a_real_unit_string'
+    with redirect_stdout(f):
+        ds.utils.change_units('home_signal_15', 'not_a_real_unit_string', verbose=True)
+    s = f.getvalue()
+    assert s.strip() == f"Unable to convert '{var_name}' to units of '{unit}'. Skipping unit converstion for '{var_name}'."
+
+    ds.close()
+    del ds
+
 
 def test_ts_weighted_average():
     ds = act.io.arm.read_arm_netcdf(act.tests.sample_files.EXAMPLE_MET_WILDCARD)