Clarify whitespace behavior in read_fwf documentation (#16772)

pandas/io/parsers.py

@@ -63,8 +63,6 @@
     file. For file URLs, a host is expected. For instance, a local file could
     be file ://localhost/path/to/table.csv
 %s
-delimiter : str, default ``None``
-    Alternative argument name for sep.
 delim_whitespace : boolean, default False
     Specifies whether or not whitespace (e.g. ``' '`` or ``'\t'``) will be
     used as the sep. Equivalent to setting ``sep='\s+'``. If this option
@@ -316,7 +314,9 @@
     be used automatically. In addition, separators longer than 1 character and
     different from ``'\s+'`` will be interpreted as regular expressions and
     will also force the use of the Python parsing engine. Note that regex
-    delimiters are prone to ignoring quoted data. Regex example: ``'\r\t'``"""
+    delimiters are prone to ignoring quoted data. Regex example: ``'\r\t'``
+delimiter : str, default ``None``
+    Alternative argument name for sep."""
 
 _read_csv_doc = """
 Read CSV (comma-separated) file into DataFrame
@@ -341,15 +341,16 @@
 widths : list of ints. optional
     A list of field widths which can be used instead of 'colspecs' if
     the intervals are contiguous.
+delimiter: str, default ``\t ``
+    Characters to consider as filler characters in the fixed-width file.
+    Can be used to specify the filler character of the fields
+    if it is not spaces (e.g., '~').
 """
 
 _read_fwf_doc = """
 Read a table of fixed-width formatted lines into DataFrame
 
 %s
-
-Also, 'delimiter' is used to specify the filler character of the
-fields if it is not spaces (e.g., '~').
 """ % (_parser_params % (_fwf_widths, ''))
 
 

pandas/tests/io/parser/test_read_fwf.py

@@ -405,3 +405,15 @@ def test_skiprows_inference_empty(self):
 
         with pytest.raises(EmptyDataError):
             read_fwf(StringIO(test), skiprows=3)
+
+    def test_whitespace_preservation(self):
+        data_expected = """ a ,bbb
+ cc,dd """
+        expected = read_csv(StringIO(data_expected), header=None)
+
+        test_data = """ a bbb
+ ccdd """
+        df = read_fwf(StringIO(test_data), widths=[3, 3],
+                      header=None, delimiter="\n")
+
+        tm.assert_frame_equal(df, expected)