ENH: add support for na_filter in Python engine

Author: gfyoung

doc/source/whatsnew/v0.18.2.txt

@@ -75,6 +75,7 @@ Other enhancements
     pd.Timestamp(year=2012, month=1, day=1, hour=8, minute=30)
 
 - The ``pd.read_csv()`` with ``engine='python'`` has gained support for the ``decimal`` option (:issue:`12933`)
+- The ``pd.read_csv()`` with ``engine='python'`` has gained support for the ``na_filter`` option (:issue:`13321`)
 
 - ``Index.astype()`` now accepts an optional boolean argument ``copy``, which allows optional copying if the requirements on dtype are satisfied (:issue:`13209`)
 - ``Index`` now supports the ``.where()`` function for same shape indexing (:issue:`13170`)

pandas/io/parsers.py

@@ -425,7 +425,6 @@ def _read(filepath_or_buffer, kwds):
 _c_unsupported = set(['skip_footer'])
 _python_unsupported = set([
     'as_recarray',
-    'na_filter',
     'compact_ints',
     'use_unsigned',
     'low_memory',
@@ -1188,8 +1187,13 @@ def _convert_to_ndarrays(self, dct, na_values, na_fvalues, verbose=False,
         result = {}
         for c, values in compat.iteritems(dct):
             conv_f = None if converters is None else converters.get(c, None)
-            col_na_values, col_na_fvalues = _get_na_values(c, na_values,
-                                                           na_fvalues)
+
+            if self.na_filter:
+                col_na_values, col_na_fvalues = _get_na_values(
+                    c, na_values, na_fvalues)
+            else:
+                col_na_values, col_na_fvalues = set(), set()
+
             coerce_type = True
             if conv_f is not None:
                 try:
@@ -1634,6 +1638,8 @@ def __init__(self, f, **kwds):
 
         self.names_passed = kwds['names'] or None
 
+        self.na_filter = kwds['na_filter']
+
         self.has_index_names = False
         if 'has_index_names' in kwds:
             self.has_index_names = kwds['has_index_names']

pandas/io/tests/parser/c_parser_only.py

@@ -61,12 +61,6 @@ def test_delim_whitespace_custom_terminator(self):
                              columns=['a', 'b', 'c'])
         tm.assert_frame_equal(df, expected)
 
-    def test_parse_dates_empty_string(self):
-        # see gh-2263
-        s = StringIO("Date, test\n2012-01-01, 1\n,2")
-        result = self.read_csv(s, parse_dates=["Date"], na_filter=False)
-        self.assertTrue(result['Date'].isnull()[1])
-
     def test_dtype_and_names_error(self):
         # see gh-8833: passing both dtype and names
         # resulting in an error reporting issue

pandas/io/tests/parser/common.py

@@ -1319,10 +1319,8 @@ def test_inf_parsing(self):
         df = self.read_csv(StringIO(data), index_col=0)
         tm.assert_almost_equal(df['A'].values, expected.values)
 
-        if self.engine == 'c':
-            # TODO: remove condition when 'na_filter' is supported for Python
-            df = self.read_csv(StringIO(data), index_col=0, na_filter=False)
-            tm.assert_almost_equal(df['A'].values, expected.values)
+        df = self.read_csv(StringIO(data), index_col=0, na_filter=False)
+        tm.assert_almost_equal(df['A'].values, expected.values)
 
     def test_raise_on_no_columns(self):
         # single newline

pandas/io/tests/parser/na_values.py

@@ -223,3 +223,21 @@ def test_na_values_keep_default(self):
                         'Three': ['None', 'two', 'None', 'nan', 'five', '',
                                   'seven']})
         tm.assert_frame_equal(xp.reindex(columns=df.columns), df)
+
+    def test_na_values_na_filter_override(self):
+        data = """\
+A,B
+1,A
+nan,B
+3,C
+"""
+
+        expected = DataFrame([[1, 'A'], [np.nan, np.nan], [3, 'C']],
+                             columns=['A', 'B'])
+        out = self.read_csv(StringIO(data), na_values=['B'], na_filter=True)
+        tm.assert_frame_equal(out, expected)
+
+        expected = DataFrame([['1', 'A'], ['nan', 'B'], ['3', 'C']],
+                             columns=['A', 'B'])
+        out = self.read_csv(StringIO(data), na_values=['B'], na_filter=False)
+        tm.assert_frame_equal(out, expected)

pandas/io/tests/parser/parse_dates.py

@@ -467,3 +467,10 @@ def test_read_with_parse_dates_invalid_type(self):
                               StringIO(data), parse_dates=np.array([4, 5]))
         tm.assertRaisesRegexp(TypeError, errmsg, self.read_csv,
                               StringIO(data), parse_dates=set([1, 3, 3]))
+
+    def test_parse_dates_empty_string(self):
+        # see gh-2263
+        data = "Date, test\n2012-01-01, 1\n,2"
+        result = self.read_csv(StringIO(data), parse_dates=["Date"],
+                               na_filter=False)
+        self.assertTrue(result['Date'].isnull()[1])