API: read_csv, to_csv line_terminator keyword inconsistency

pandas/core/generic.py

@@ -3065,6 +3065,7 @@ def to_csv(
         decimal: Optional[str] = ".",
         errors: str = "strict",
         storage_options: StorageOptions = None,
+        **kwargs,
     ) -> Optional[str]:
         r"""
         Write object to a comma-separated values (csv) file.
@@ -3179,9 +3180,6 @@ def to_csv(
             Specifies how encoding and decoding errors are to be handled.
             See the errors argument for :func:`open` for a full list
             of options.
-
-            .. versionadded:: 1.1.0
-
         storage_options : dict, optional
             Extra options that make sense for a particular storage connection, e.g.
             host, port, username, password, etc., if using a URL that will
@@ -3190,6 +3188,11 @@ def to_csv(
             a file-like buffer. See the fsspec and backend storage implementation
             docs for the set of allowed keys and values
 
+            .. versionadded:: 1.2.0
+        kwargs
+            Additional keyword arguments passed to ``pd.to_csv`` for compatibility
+            with `csv` module. Include `lineterminator` (an alias of `line_terminator`).
+
             .. versionadded:: 1.2.0
 
         Returns

pandas/io/parsers.py

@@ -27,7 +27,7 @@
     ParserError,
     ParserWarning,
 )
-from pandas.util._decorators import Appender
+from pandas.util._decorators import Appender, _get_alias_from_kwargs
 
 from pandas.core.dtypes.cast import astype_nansafe
 from pandas.core.dtypes.common import (
@@ -285,7 +285,7 @@
     Thousands separator.
 decimal : str, default '.'
     Character to recognize as decimal point (e.g. use ',' for European data).
-lineterminator : str (length 1), optional
+line_terminator : str (length 1), optional
     Character to break file into lines. Only valid with C parser.
 quotechar : str (length 1), optional
     The character used to denote the start and end of a quoted item. Quoted
@@ -346,6 +346,11 @@
     values. The options are `None` for the ordinary converter,
     `high` for the high-precision converter, and `round_trip` for the
     round-trip converter.
+kwargs
+    Additional keyword arguments passed to ``pd.read_csv`` for compatibility
+    with `csv` module. Include `lineterminator` (an alias of `line_terminator`).
+
+    .. versionadded:: 1.2.0
 
 Returns
 -------
@@ -580,7 +585,7 @@ def read_csv(
     compression="infer",
     thousands=None,
     decimal: str = ".",
-    lineterminator=None,
+    line_terminator=None,
     quotechar='"',
     quoting=csv.QUOTE_MINIMAL,
     doublequote=True,
@@ -597,6 +602,7 @@ def read_csv(
     memory_map=False,
     float_precision=None,
     storage_options=None,
+    **kwargs,
 ):
     # gh-23761
     #
@@ -634,6 +640,8 @@ def read_csv(
         engine = "c"
         engine_specified = False
 
+    kwargs.setdefault("lineterminator", line_terminator)
+
     kwds.update(
         delimiter=delimiter,
         engine=engine,
@@ -645,7 +653,6 @@ def read_csv(
         quotechar=quotechar,
         quoting=quoting,
         skipinitialspace=skipinitialspace,
-        lineterminator=lineterminator,
         header=header,
         index_col=index_col,
         names=names,
@@ -684,6 +691,7 @@ def read_csv(
         infer_datetime_format=infer_datetime_format,
         skip_blank_lines=skip_blank_lines,
         storage_options=storage_options,
+        **kwargs,
     )
 
     return _read(filepath_or_buffer, kwds)

pandas/tests/frame/test_to_csv.py

@@ -1,6 +1,7 @@
 import csv
 from io import StringIO
 import os
+import re
 
 import numpy as np
 import pytest
@@ -998,6 +999,45 @@ def test_to_csv_line_terminators(self):
             with open(path, mode="rb") as f:
                 assert f.read() == expected
 
+    def test_to_csv_lineterminator_alternative_args(self):
+        # GH 9568
+        # examples from test_to_csv_line_terminators
+        # test equivalence of line_terminator vs. lineterminator keyword args
+
+        df = DataFrame({"A": [1, 2, 3], "B": [4, 5, 6]}, index=["one", "two", "three"])
+
+        # case 1: CRLF as line terminator
+
+        with tm.ensure_clean() as path:
+            df.to_csv(path, line_terminator="\r\n")
+
+            with open(path, mode="rb") as f:
+                res_line_terminator = f.read()
+
+        with tm.ensure_clean() as path:
+            df.to_csv(path, lineterminator="\r\n")
+
+            with open(path, mode="rb") as f:
+                res_lineterminator = f.read()
+
+        assert re.match(res_line_terminator, res_lineterminator)
+
+        # case 2: LF as line terminator
+
+        with tm.ensure_clean() as path:
+            df.to_csv(path, line_terminator="\n")
+
+            with open(path, mode="rb") as f:
+                res_line_terminator = f.read()
+
+        with tm.ensure_clean() as path:
+            df.to_csv(path, lineterminator="\n")
+
+            with open(path, mode="rb") as f:
+                res_lineterminator = f.read()
+
+        assert re.match(res_line_terminator, res_lineterminator)
+
     def test_to_csv_from_csv_categorical(self):
 
         # CSV with categoricals should result in the same output

pandas/tests/io/formats/test_to_csv.py

@@ -1,5 +1,6 @@
 import io
 import os
+import re
 import sys
 
 import numpy as np
@@ -330,10 +331,15 @@ def test_to_csv_multi_index(self):
     @pytest.mark.parametrize("klass", [pd.DataFrame, pd.Series])
     def test_to_csv_single_level_multi_index(self, ind, expected, klass):
         # see gh-19589
-        result = klass(pd.Series([1], ind, name="data")).to_csv(
+        # GH9568 test for equivalence between line_terminator and lineterminator
+        result_line_terminator = klass(pd.Series([1], ind, name="data")).to_csv(
             line_terminator="\n", header=True
         )
-        assert result == expected
+        result_lineterminator = klass(pd.Series([1], ind, name="data")).to_csv(
+            lineterminator="\n", header=True
+        )
+        assert re.match(result_lineterminator, result_line_terminator)
+        assert re.match(result_line_terminator, expected)
 
     def test_to_csv_string_array_ascii(self):
         # GH 10813
@@ -436,6 +442,25 @@ def test_to_csv_string_with_crlf(self):
             with open(path, "rb") as f:
                 assert f.read() == expected_crlf
 
+    def test_to_csv_string_line_terminator_alternative_args(self):
+        # GH 9568
+        # test equivalence of line_terminator vs. lineterminator keyword args
+
+        data = {"int": [1, 2, 3], "str_lf": ["abc", "d\nef", "g\nh\n\ni"]}
+        df = pd.DataFrame(data)
+
+        with tm.ensure_clean("crlf_test.csv") as path:
+            df.to_csv(path, line_terminator="\n", index=False)
+            with open(path, "rb") as f:
+                res_line_terminator = f.read()
+
+        with tm.ensure_clean("crlf_test.csv") as path:
+            df.to_csv(path, lineterminator="\n", index=False)
+            with open(path, "rb") as f:
+                res_lineterminator = f.read()
+
+        assert re.match(res_line_terminator, res_lineterminator)
+
     def test_to_csv_stdout_file(self, capsys):
         # GH 21561
         df = pd.DataFrame(

pandas/tests/io/parser/test_common.py

@@ -2080,8 +2080,6 @@ def test_unexpected_keyword_parameter_exception(all_parsers):
     parser = all_parsers
 
     msg = "{}\\(\\) got an unexpected keyword argument 'foo'"
-    with pytest.raises(TypeError, match=msg.format("read_csv")):
-        parser.read_csv("foo.csv", foo=1)
     with pytest.raises(TypeError, match=msg.format("read_table")):
         parser.read_table("foo.tsv", foo=1)