refactoring and adding docstring and test cases

Author: charlesdong1991

pandas/core/generic.py

@@ -2871,7 +2871,7 @@ def to_latex(self, buf=None, columns=None, col_space=None, header=True,
             return formatter.buf.getvalue()
 
     def to_csv(self, path_or_buf=None, sep=",", na_rep='', float_format=None,
-               columns=None, header=True, index=True, index_label=True,
+               columns=None, header=True, index=True, index_label=None,
                mode='w', encoding=None, compression='infer', quoting=None,
                quotechar='"', line_terminator=None, chunksize=None,
                tupleize_cols=None, date_format=None, doublequote=True,
@@ -2910,10 +2910,11 @@ def to_csv(self, path_or_buf=None, sep=",", na_rep='', float_format=None,
 
         index : bool, default True
             Write row names (index).
-        index_label : bool or str or sequence, default True.
-            Column label for index column(s) if desired. If header or index
-            is False, index_label will be set to False. A sequence should be
-            given if the object uses MultiIndex. If False do not print fields
+        index_label : bool or str or sequence, default None.
+            If index_label is not explicitly called, False if either header
+            or index is set to False; otherwise, True. If index_label is
+            explicitly called by allowed types of input, then input will be
+            given to index_label. If False, do not print fields
             for index names. Use index_label=False for easier importing in R.
         mode : str
             Python write mode, default 'w'.

pandas/io/formats/csvs.py

@@ -29,7 +29,7 @@ class CSVFormatter(object):
 
     def __init__(self, obj, path_or_buf=None, sep=",", na_rep='',
                  float_format=None, cols=None, header=True, index=True,
-                 index_label=True, mode='w', nanRep=None, encoding=None,
+                 index_label=None, mode='w', nanRep=None, encoding=None,
                  compression='infer', quoting=None, line_terminator='\n',
                  chunksize=None, tupleize_cols=False, quotechar='"',
                  date_format=None, doublequote=True, escapechar=None,
@@ -50,15 +50,17 @@ def __init__(self, obj, path_or_buf=None, sep=",", na_rep='',
 
         self.header = header
         self.index = index
-        self.index_label = index_label
-        # set defualt index label to False if header is False and if
-        # index_label is boolean.
-        if self.header is None or self.header is False:
-            if isinstance(self.index_label, bool):
+        # if index label is not explicitly called, index label is True if header
+        # or index is not False; otherwise, index label is set to False
+        if index_label is None:
+            if self.header is False or self.header is None or not self.index:
                 self.index_label = False
-        # set index label to False if index is False.
-        if not self.index:
-            self.index_label = False
+            else:
+                self.index_label = True
+        else:
+            # if index label is explicitly called, then use the caller.
+            self.index_label = index_label
+
         self.mode = mode
         if encoding is None:
             encoding = 'ascii' if compat.PY2 else 'utf-8'

pandas/tests/generic/test_frame.py

@@ -274,10 +274,12 @@ def test_deepcopy_empty(self):
     @pytest.mark.skipif(os.name == 'nt',
                         reason="Windows use \r\n for newline")
     @pytest.mark.parametrize("header, index_label, expected", [
-        (False, True, '0,0,0\n1,0,0\n'),
+        (False, True, 'index.name,,\n0,0,0\n1,0,0\n'),
         (True, True, 'index.name,0,1\n0,0,0\n1,0,0\n'),
         (False, False, '0,0,0\n1,0,0\n'),
-        (True, False, ',0,1\n0,0,0\n1,0,0\n')
+        (True, False, ',0,1\n0,0,0\n1,0,0\n'),
+        (False, None, '0,0,0\n1,0,0\n'),
+        (True, None, 'index.name,0,1\n0,0,0\n1,0,0\n')
     ])
     def test_to_csv_header_single_index(self, header, index_label, expected):
         # issue 24546
@@ -290,10 +292,12 @@ def test_to_csv_header_single_index(self, header, index_label, expected):
     @pytest.mark.skipif(os.name == 'nt',
                         reason="Windows use \r\n for newline")
     @pytest.mark.parametrize("header, index_label, expected", [
-        (False, True, 'a,b,0,0\na,c,0,0\n'),
+        (False, True, 'index.name.0,index.name.1,,\na,b,0,0\na,c,0,0\n'),
         (True, True, 'index.name.0,index.name.1,0,1\na,b,0,0\na,c,0,0\n'),
         (False, False, 'a,b,0,0\na,c,0,0\n'),
-        (True, False, ',,0,1\na,b,0,0\na,c,0,0\n')
+        (True, False, ',,0,1\na,b,0,0\na,c,0,0\n'),
+        (False, None, 'a,b,0,0\na,c,0,0\n'),
+        (True, None, 'index.name.0,index.name.1,0,1\na,b,0,0\na,c,0,0\n')
     ])
     def test_to_csv_header_multi_index(self, header, index_label, expected):
         # issue 24546