fix(flopy/utils/sfroutputfile.py::SfrFile.get_results): refactor deprecated DataFrame.append() call to pandas.concat() (#2491)

Refactor deprecated DataFrame.append() call to pandas.concat()

Author: aleaf

autotest/test_sfr.py

@@ -7,6 +7,7 @@
 import matplotlib
 import matplotlib.pyplot as plt
 import numpy as np
+import pandas as pd
 import pytest
 from modflow_devtools.markers import requires_exe, requires_pkg
 
@@ -675,6 +676,13 @@ def test_SfrFile(function_tmpdir, sfr_examples_path, mf2005_model_path):
     assert df.column.values[0] == 169
     assert df.Cond.values[0] == 74510.0
     assert df.gw_head.values[3] == 1.288e03
+    
+    segments = [1, 2, 3]
+    reaches = [3, 3, 3]
+    subset_df = sfrout.get_results(segments, reaches)
+    expected = pd.concat([df.loc[(df['segment'] == s) & (df['reach'] == r)] 
+                          for s, r in zip(segments, reaches)])
+    subset_df.equals(expected)
 
     sfrout = SfrFile(sfr_examples_path / "test1tr.flw")
     assert sfrout.ncol == 16, sfrout.ncol

flopy/utils/sfroutputfile.py

@@ -245,7 +245,7 @@ def get_results(self, segment, reach):
             for s, r in locsr:
                 srresults = self._get_result(s, r)
                 if len(srresults) > 0:
-                    results = results.append(srresults)
+                    results = pd.concat([results, srresults])
                 else:
                     print(f"No results for segment {s}, reach {r}!")
         return results