From 4281f16001ed5d861538c684d2728f93f0eba2d2 Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Sat, 15 Aug 2020 16:16:56 +0200
Subject: [PATCH 01/19] DEPR: Deprecate parse_date_time in
 pandas.io.date_converters and update tests

---
 doc/source/user_guide/io.rst               |  2 +-
 pandas/io/date_converters.py               | 23 +++++++++++++++++++---
 pandas/tests/io/parser/test_parse_dates.py |  6 +++---
 pandas/tests/io/test_date_converters.py    |  7 ++++---
 4 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/doc/source/user_guide/io.rst b/doc/source/user_guide/io.rst
index d4be9d802d697..aa6529b3a76d6 100644
--- a/doc/source/user_guide/io.rst
+++ b/doc/source/user_guide/io.rst
@@ -927,7 +927,7 @@ take full advantage of the flexibility of the date parsing API:
 .. ipython:: python
 
    df = pd.read_csv('tmp.csv', header=None, parse_dates=date_spec,
-                    date_parser=pd.io.date_converters.parse_date_time)
+                    date_parser=pd.to_datetime)
    df
 
 Pandas will try to call the ``date_parser`` function in three different ways. If
diff --git a/pandas/io/date_converters.py b/pandas/io/date_converters.py
index 07919dbda63ae..9e3f0a9d1b807 100644
--- a/pandas/io/date_converters.py
+++ b/pandas/io/date_converters.py
@@ -1,13 +1,30 @@
 """This module is designed for community supported date conversion functions"""
+import warnings
+
 import numpy as np
 
 from pandas._libs.tslibs import parsing
 
+from pandas import to_datetime
+
 
 def parse_date_time(date_col, time_col):
-    date_col = _maybe_cast(date_col)
-    time_col = _maybe_cast(time_col)
-    return parsing.try_parse_date_and_time(date_col, time_col)
+    """Convert separate columns with dates and times into a single datetime column
+
+    .. deprecated:: 1.1.0
+       Use pd.to_datetime(date_col + " " + time_col) instead to get a Pandas Series.
+       Use pd.to_datetime(date_col + " " + time_col).to_pydatetime() instead to get
+        a Numpy array.
+    """
+    warnings.warn(
+        """
+        Use pd.to_datetime(date_col + " " + time_col) instead to get a Pandas Series.
+        Use pd.to_datetime(date_col + " " + time_col).to_pydatetime() instead to get a Numpy array.
+""",  # noqa: E501
+        FutureWarning,
+        stacklevel=2,
+    )
+    return to_datetime(date_col + " " + time_col).to_pydatetime()
 
 
 def parse_date_fields(year_col, month_col, day_col):
diff --git a/pandas/tests/io/parser/test_parse_dates.py b/pandas/tests/io/parser/test_parse_dates.py
index ed947755e3419..3262e29b1a83e 100644
--- a/pandas/tests/io/parser/test_parse_dates.py
+++ b/pandas/tests/io/parser/test_parse_dates.py
@@ -385,7 +385,7 @@ def test_multiple_date_cols_int_cast(all_parsers):
     result = parser.read_csv(
         StringIO(data),
         header=None,
-        date_parser=conv.parse_date_time,
+        date_parser=pd.to_datetime,
         parse_dates=parse_dates,
         prefix="X",
     )
@@ -1178,7 +1178,7 @@ def test_parse_date_time_multi_level_column_name(all_parsers):
         StringIO(data),
         header=[0, 1],
         parse_dates={"date_time": [0, 1]},
-        date_parser=conv.parse_date_time,
+        date_parser=pd.to_datetime,
     )
 
     expected_data = [
@@ -1263,7 +1263,7 @@ def test_parse_date_time_multi_level_column_name(all_parsers):
 )
 def test_parse_date_time(all_parsers, data, kwargs, expected):
     parser = all_parsers
-    result = parser.read_csv(StringIO(data), date_parser=conv.parse_date_time, **kwargs)
+    result = parser.read_csv(StringIO(data), date_parser=pd.to_datetime, **kwargs)
 
     # Python can sometimes be flaky about how
     # the aggregated columns are entered, so
diff --git a/pandas/tests/io/test_date_converters.py b/pandas/tests/io/test_date_converters.py
index cdb8eca02a3e5..27b2e6a409629 100644
--- a/pandas/tests/io/test_date_converters.py
+++ b/pandas/tests/io/test_date_converters.py
@@ -8,12 +8,13 @@
 
 
 def test_parse_date_time():
+
     dates = np.array(["2007/1/3", "2008/2/4"], dtype=object)
     times = np.array(["05:07:09", "06:08:00"], dtype=object)
     expected = np.array([datetime(2007, 1, 3, 5, 7, 9), datetime(2008, 2, 4, 6, 8, 0)])
-
-    result = conv.parse_date_time(dates, times)
-    tm.assert_numpy_array_equal(result, expected)
+    with tm.assert_produces_warning(FutureWarning):
+        result = conv.parse_date_time(dates, times)
+        tm.assert_numpy_array_equal(result, expected)
 
 
 def test_parse_date_fields():

From 852d4d9e8aff76eddb0dac2b24c32ee624fb3bc1 Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Sat, 15 Aug 2020 17:37:25 +0200
Subject: [PATCH 02/19] DEPR: Deprecate parse_date_fields in
 pandas.io.date_converters and update tests

---
 pandas/io/date_converters.py               | 24 ++++++++++++++++++----
 pandas/tests/io/parser/test_parse_dates.py |  2 +-
 pandas/tests/io/test_date_converters.py    |  7 ++++---
 3 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/pandas/io/date_converters.py b/pandas/io/date_converters.py
index 9e3f0a9d1b807..a13dab6e5a492 100644
--- a/pandas/io/date_converters.py
+++ b/pandas/io/date_converters.py
@@ -28,10 +28,26 @@ def parse_date_time(date_col, time_col):
 
 
 def parse_date_fields(year_col, month_col, day_col):
-    year_col = _maybe_cast(year_col)
-    month_col = _maybe_cast(month_col)
-    day_col = _maybe_cast(day_col)
-    return parsing.try_parse_year_month_day(year_col, month_col, day_col)
+    """Convert separate columns with years, months and days into a single date column
+
+    .. deprecated:: 1.1.0
+        Use pd.to_datetime({"year": year_col, "month": month_col, "day": day_col})
+        instead to get a Pandas Series.
+        Use ser = pd.to_datetime({"year": year_col, "month": month_col, "day": day_col})
+        and np.array([s.to_pydatetime() for s in ser]) instead to get a Numpy array.
+    """
+    warnings.warn(
+        """
+        Use pd.to_datetime({"year": year_col, "month": month_col, "day": day_col}) instead to get a Pandas Series.
+        Use ser = pd.to_datetime({"year": year_col, "month": month_col, "day": day_col}) and
+        np.array([s.to_pydatetime() for s in ser]) instead to get a Numpy array.
+""",  # noqa: E501
+        FutureWarning,
+        stacklevel=2,
+    )
+
+    ser = to_datetime({"year": year_col, "month": month_col, "day": day_col})
+    return np.array([s.to_pydatetime() for s in ser])
 
 
 def parse_all_fields(year_col, month_col, day_col, hour_col, minute_col, second_col):
diff --git a/pandas/tests/io/parser/test_parse_dates.py b/pandas/tests/io/parser/test_parse_dates.py
index 3262e29b1a83e..bc63fcb860fda 100644
--- a/pandas/tests/io/parser/test_parse_dates.py
+++ b/pandas/tests/io/parser/test_parse_dates.py
@@ -1279,7 +1279,7 @@ def test_parse_date_fields(all_parsers):
         StringIO(data),
         header=0,
         parse_dates={"ymd": [0, 1, 2]},
-        date_parser=conv.parse_date_fields,
+        date_parser=pd.to_datetime,
     )
 
     expected = DataFrame(
diff --git a/pandas/tests/io/test_date_converters.py b/pandas/tests/io/test_date_converters.py
index 27b2e6a409629..1d4e93debea75 100644
--- a/pandas/tests/io/test_date_converters.py
+++ b/pandas/tests/io/test_date_converters.py
@@ -21,10 +21,11 @@ def test_parse_date_fields():
     days = np.array([3, 4])
     months = np.array([1, 2])
     years = np.array([2007, 2008])
-    result = conv.parse_date_fields(years, months, days)
-
     expected = np.array([datetime(2007, 1, 3), datetime(2008, 2, 4)])
-    tm.assert_numpy_array_equal(result, expected)
+
+    with tm.assert_produces_warning(FutureWarning):
+        result = conv.parse_date_fields(years, months, days)
+        tm.assert_numpy_array_equal(result, expected)
 
 
 def test_parse_all_fields():

From eed8f16b54f873f84007104abd4c76f62d2416eb Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Sat, 15 Aug 2020 17:49:05 +0200
Subject: [PATCH 03/19] DEPR: Deprecate parse_all_fields in
 pandas.io.date_converters and update tests

---
 pandas/io/date_converters.py               | 45 +++++++++++++++++-----
 pandas/tests/io/parser/test_parse_dates.py |  8 ++--
 pandas/tests/io/test_date_converters.py    |  7 ++--
 3 files changed, 43 insertions(+), 17 deletions(-)

diff --git a/pandas/io/date_converters.py b/pandas/io/date_converters.py
index a13dab6e5a492..3be8a0f4e7992 100644
--- a/pandas/io/date_converters.py
+++ b/pandas/io/date_converters.py
@@ -3,8 +3,6 @@
 
 import numpy as np
 
-from pandas._libs.tslibs import parsing
-
 from pandas import to_datetime
 
 
@@ -51,16 +49,43 @@ def parse_date_fields(year_col, month_col, day_col):
 
 
 def parse_all_fields(year_col, month_col, day_col, hour_col, minute_col, second_col):
-    year_col = _maybe_cast(year_col)
-    month_col = _maybe_cast(month_col)
-    day_col = _maybe_cast(day_col)
-    hour_col = _maybe_cast(hour_col)
-    minute_col = _maybe_cast(minute_col)
-    second_col = _maybe_cast(second_col)
-    return parsing.try_parse_datetime_components(
-        year_col, month_col, day_col, hour_col, minute_col, second_col
+    """Convert separate columns with years, months, days, hours, minutes and seconds
+     into a single datetime column
+
+    .. deprecated:: 1.1.0
+        Use pd.to_datetime({"year": year_col, "month": month_col, "day": day_col,
+        "hour": hour_col, "minute": minute_col, second": second_col}) instead to get
+        a Pandas Series.
+        Use ser = pd.to_datetime({"year": year_col, "month": month_col, "day": day_col,
+        "hour": hour_col, "minute": minute_col, second": second_col}) and
+        np.array([s.to_pydatetime() for s in ser]) instead to get a Numpy array.
+    """
+
+    warnings.warn(
+        """
+        Use pd.to_datetime({"year": year_col, "month": month_col, "day": day_col,
+        "hour": hour_col, "minute": minute_col, second": second_col}) instead to get a Pandas Series.
+        Use ser = pd.to_datetime({"year": year_col, "month": month_col, "day": day_col,
+        "hour": hour_col, "minute": minute_col, second": second_col}) and
+        np.array([s.to_pydatetime() for s in ser]) instead to get a Numpy array.
+""",  # noqa: E501
+        FutureWarning,
+        stacklevel=2,
     )
 
+    ser = to_datetime(
+        {
+            "year": year_col,
+            "month": month_col,
+            "day": day_col,
+            "hour": hour_col,
+            "minute": minute_col,
+            "second": second_col,
+        }
+    )
+
+    return np.array([s.to_pydatetime() for s in ser])
+
 
 def generic_parser(parse_func, *cols):
     N = _check_columns(cols)
diff --git a/pandas/tests/io/parser/test_parse_dates.py b/pandas/tests/io/parser/test_parse_dates.py
index bc63fcb860fda..2d362d949756e 100644
--- a/pandas/tests/io/parser/test_parse_dates.py
+++ b/pandas/tests/io/parser/test_parse_dates.py
@@ -23,8 +23,6 @@
 import pandas._testing as tm
 from pandas.core.indexes.datetimes import date_range
 
-import pandas.io.date_converters as conv
-
 # constant
 _DEFAULT_DATETIME = datetime(1, 1, 1)
 
@@ -1290,6 +1288,7 @@ def test_parse_date_fields(all_parsers):
 
 
 def test_parse_date_all_fields(all_parsers):
+
     parser = all_parsers
     data = """\
 year,month,day,hour,minute,second,a,b
@@ -1299,7 +1298,7 @@ def test_parse_date_all_fields(all_parsers):
     result = parser.read_csv(
         StringIO(data),
         header=0,
-        date_parser=conv.parse_all_fields,
+        date_parser=lambda x: pd.to_datetime(x, format="%Y %m %d %H %M %S"),
         parse_dates={"ymdHMS": [0, 1, 2, 3, 4, 5]},
     )
     expected = DataFrame(
@@ -1322,7 +1321,8 @@ def test_datetime_fractional_seconds(all_parsers):
     result = parser.read_csv(
         StringIO(data),
         header=0,
-        date_parser=conv.parse_all_fields,
+        # date_parser=conv.parse_all_fields,
+        date_parser=lambda x: pd.to_datetime(x, format="%Y %m %d %H %M %S.%f"),
         parse_dates={"ymdHMS": [0, 1, 2, 3, 4, 5]},
     )
     expected = DataFrame(
diff --git a/pandas/tests/io/test_date_converters.py b/pandas/tests/io/test_date_converters.py
index 1d4e93debea75..4fb53decfd887 100644
--- a/pandas/tests/io/test_date_converters.py
+++ b/pandas/tests/io/test_date_converters.py
@@ -36,7 +36,8 @@ def test_parse_all_fields():
     days = np.array([3, 4])
     years = np.array([2007, 2008])
     months = np.array([1, 2])
-
-    result = conv.parse_all_fields(years, months, days, hours, minutes, seconds)
     expected = np.array([datetime(2007, 1, 3, 5, 7, 9), datetime(2008, 2, 4, 6, 8, 0)])
-    tm.assert_numpy_array_equal(result, expected)
+
+    with tm.assert_produces_warning(FutureWarning):
+        result = conv.parse_all_fields(years, months, days, hours, minutes, seconds)
+        tm.assert_numpy_array_equal(result, expected)

From 65ec57007b31055547eaa05425a799bf7490e2a5 Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Sat, 15 Aug 2020 20:08:57 +0200
Subject: [PATCH 04/19] DEPR: Deprecate generic_parser in
 pandas.io.date_converters

---
 pandas/io/date_converters.py | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/pandas/io/date_converters.py b/pandas/io/date_converters.py
index 3be8a0f4e7992..88ba1764dbc02 100644
--- a/pandas/io/date_converters.py
+++ b/pandas/io/date_converters.py
@@ -88,6 +88,20 @@ def parse_all_fields(year_col, month_col, day_col, hour_col, minute_col, second_
 
 
 def generic_parser(parse_func, *cols):
+    """Parse single row of values into a datetime
+
+    .. deprecated:: 1.1.0
+        Use pd.to_datetime.
+    """
+
+    warnings.warn(
+        """
+        Use pd.to_datetime instead.
+""",  # noqa: E501
+        FutureWarning,
+        stacklevel=2,
+    )
+
     N = _check_columns(cols)
     results = np.empty(N, dtype=object)
 
@@ -98,12 +112,6 @@ def generic_parser(parse_func, *cols):
     return results
 
 
-def _maybe_cast(arr):
-    if not arr.dtype.type == np.object_:
-        arr = np.array(arr, dtype=object)
-    return arr
-
-
 def _check_columns(cols):
     if not len(cols):
         raise AssertionError("There must be at least 1 column")

From 344e5de336e6c4dc84fef2b9f1af9a29794f2c06 Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Sat, 15 Aug 2020 20:19:07 +0200
Subject: [PATCH 05/19] DOC: Update docstrings

---
 pandas/io/date_converters.py | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/pandas/io/date_converters.py b/pandas/io/date_converters.py
index 88ba1764dbc02..55777f77e4296 100644
--- a/pandas/io/date_converters.py
+++ b/pandas/io/date_converters.py
@@ -7,7 +7,8 @@
 
 
 def parse_date_time(date_col, time_col):
-    """Convert separate columns with dates and times into a single datetime column
+    """
+    Parse columns with dates and times into a single datetime column.
 
     .. deprecated:: 1.1.0
        Use pd.to_datetime(date_col + " " + time_col) instead to get a Pandas Series.
@@ -26,7 +27,8 @@ def parse_date_time(date_col, time_col):
 
 
 def parse_date_fields(year_col, month_col, day_col):
-    """Convert separate columns with years, months and days into a single date column
+    """
+    Parse columns with years, months and days into a single date column.
 
     .. deprecated:: 1.1.0
         Use pd.to_datetime({"year": year_col, "month": month_col, "day": day_col})
@@ -49,8 +51,8 @@ def parse_date_fields(year_col, month_col, day_col):
 
 
 def parse_all_fields(year_col, month_col, day_col, hour_col, minute_col, second_col):
-    """Convert separate columns with years, months, days, hours, minutes and seconds
-     into a single datetime column
+    """
+    Parse columns with datetime information into a single datetime column.
 
     .. deprecated:: 1.1.0
         Use pd.to_datetime({"year": year_col, "month": month_col, "day": day_col,
@@ -88,10 +90,11 @@ def parse_all_fields(year_col, month_col, day_col, hour_col, minute_col, second_
 
 
 def generic_parser(parse_func, *cols):
-    """Parse single row of values into a datetime
+    """
+    Use dateparser to parse columns with data information into a single datetime column.
 
     .. deprecated:: 1.1.0
-        Use pd.to_datetime.
+        Use pd.to_datetime instead.
     """
 
     warnings.warn(

From 04d3416d3c3731cb9e1e4d6a43b468fd00adba87 Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Sat, 15 Aug 2020 20:32:56 +0200
Subject: [PATCH 06/19] DOC: remove mentions of the generic_parser
 functionality in the documenation

---
 doc/source/user_guide/io.rst | 13 -------------
 1 file changed, 13 deletions(-)

diff --git a/doc/source/user_guide/io.rst b/doc/source/user_guide/io.rst
index aa6529b3a76d6..c73ce4cc349eb 100644
--- a/doc/source/user_guide/io.rst
+++ b/doc/source/user_guide/io.rst
@@ -939,11 +939,6 @@ an exception is raised, the next one is tried:
 2. If #1 fails, ``date_parser`` is called with all the columns
    concatenated row-wise into a single array (e.g., ``date_parser(['2013 1', '2013 2'])``).
 
-3. If #2 fails, ``date_parser`` is called once for every row with one or more
-   string arguments from the columns indicated with `parse_dates`
-   (e.g., ``date_parser('2013', '1')`` for the first row, ``date_parser('2013', '2')``
-   for the second, etc.).
-
 Note that performance-wise, you should try these methods of parsing dates in order:
 
 1. Try to infer the format using ``infer_datetime_format=True`` (see section below).
@@ -955,14 +950,6 @@ Note that performance-wise, you should try these methods of parsing dates in ord
    For optimal performance, this should be vectorized, i.e., it should accept arrays
    as arguments.
 
-You can explore the date parsing functionality in
-`date_converters.py <https://github.com/pandas-dev/pandas/blob/master/pandas/io/date_converters.py>`__
-and add your own. We would love to turn this module into a community supported
-set of date/time parsers. To get you started, ``date_converters.py`` contains
-functions to parse dual date and time columns, year/month/day columns,
-and year/month/day/hour/minute/second columns. It also contains a
-``generic_parser`` function so you can curry it with a function that deals with
-a single date rather than the entire array.
 
 .. ipython:: python
    :suppress:

From 3df6bf975542950b54592caf4feea8f6c9881eb4 Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Sat, 15 Aug 2020 20:47:46 +0200
Subject: [PATCH 07/19] CLN: remove date_parser argument from test where it is
 not necessary

---
 pandas/tests/io/parser/test_parse_dates.py | 20 ++++----------------
 1 file changed, 4 insertions(+), 16 deletions(-)

diff --git a/pandas/tests/io/parser/test_parse_dates.py b/pandas/tests/io/parser/test_parse_dates.py
index 2d362d949756e..928cf11650722 100644
--- a/pandas/tests/io/parser/test_parse_dates.py
+++ b/pandas/tests/io/parser/test_parse_dates.py
@@ -381,11 +381,7 @@ def test_multiple_date_cols_int_cast(all_parsers):
     parser = all_parsers
 
     result = parser.read_csv(
-        StringIO(data),
-        header=None,
-        date_parser=pd.to_datetime,
-        parse_dates=parse_dates,
-        prefix="X",
+        StringIO(data), header=None, parse_dates=parse_dates, prefix="X",
     )
     expected = DataFrame(
         [
@@ -1173,10 +1169,7 @@ def test_parse_date_time_multi_level_column_name(all_parsers):
 """
     parser = all_parsers
     result = parser.read_csv(
-        StringIO(data),
-        header=[0, 1],
-        parse_dates={"date_time": [0, 1]},
-        date_parser=pd.to_datetime,
+        StringIO(data), header=[0, 1], parse_dates={"date_time": [0, 1]},
     )
 
     expected_data = [
@@ -1261,7 +1254,7 @@ def test_parse_date_time_multi_level_column_name(all_parsers):
 )
 def test_parse_date_time(all_parsers, data, kwargs, expected):
     parser = all_parsers
-    result = parser.read_csv(StringIO(data), date_parser=pd.to_datetime, **kwargs)
+    result = parser.read_csv(StringIO(data), **kwargs)
 
     # Python can sometimes be flaky about how
     # the aggregated columns are entered, so
@@ -1273,12 +1266,7 @@ def test_parse_date_time(all_parsers, data, kwargs, expected):
 def test_parse_date_fields(all_parsers):
     parser = all_parsers
     data = "year,month,day,a\n2001,01,10,10.\n2001,02,1,11."
-    result = parser.read_csv(
-        StringIO(data),
-        header=0,
-        parse_dates={"ymd": [0, 1, 2]},
-        date_parser=pd.to_datetime,
-    )
+    result = parser.read_csv(StringIO(data), header=0, parse_dates={"ymd": [0, 1, 2]},)
 
     expected = DataFrame(
         [[datetime(2001, 1, 10), 10.0], [datetime(2001, 2, 1), 11.0]],

From c995111b4e8818b412d41172102a5c693e878c0f Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Sat, 15 Aug 2020 22:41:52 +0200
Subject: [PATCH 08/19] TYP: Add MutableMapping to type hinting for
 pd.to_datetime

---
 pandas/core/tools/datetimes.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/pandas/core/tools/datetimes.py b/pandas/core/tools/datetimes.py
index 0adab143f6052..1b80dff2ff1a8 100644
--- a/pandas/core/tools/datetimes.py
+++ b/pandas/core/tools/datetimes.py
@@ -6,6 +6,7 @@
     TYPE_CHECKING,
     Callable,
     List,
+    MutableMapping,
     Optional,
     Tuple,
     TypeVar,
@@ -59,7 +60,7 @@
 # ---------------------------------------------------------------------
 # types used in annotations
 
-ArrayConvertible = Union[List, Tuple, ArrayLike, "Series"]
+ArrayConvertible = Union[List, Tuple, ArrayLike, "Series", MutableMapping]
 Scalar = Union[int, float, str]
 DatetimeScalar = TypeVar("DatetimeScalar", Scalar, datetime)
 DatetimeScalarOrArrayConvertible = Union[DatetimeScalar, ArrayConvertible]

From ef02e73a0dba366c7ff7f4d4cc5cf9039b40b55b Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Sat, 15 Aug 2020 23:30:04 +0200
Subject: [PATCH 09/19] ENH: Add overloading to pd.to_datetime for
 MutableMapping

---
 pandas/core/tools/datetimes.py | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/pandas/core/tools/datetimes.py b/pandas/core/tools/datetimes.py
index 1b80dff2ff1a8..1eb8ee4434d39 100644
--- a/pandas/core/tools/datetimes.py
+++ b/pandas/core/tools/datetimes.py
@@ -585,6 +585,23 @@ def to_datetime(
     ...
 
 
+@overload
+def to_datetime(
+    arg: MutableMapping,
+    errors: str = ...,
+    dayfirst: bool = ...,
+    yearfirst: bool = ...,
+    utc: Optional[bool] = ...,
+    format: Optional[str] = ...,
+    exact: bool = ...,
+    unit: Optional[str] = ...,
+    infer_datetime_format: bool = ...,
+    origin=...,
+    cache: bool = ...,
+) -> "Series":
+    ...
+
+
 @overload
 def to_datetime(
     arg: Union[List, Tuple],

From 3376f49e75854a3f5bbd7dae9f79645baa9a2a6f Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Tue, 18 Aug 2020 21:37:33 +0200
Subject: [PATCH 10/19] TST: Update tests where generic_parser is used

---
 pandas/tests/io/parser/test_parse_dates.py | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/pandas/tests/io/parser/test_parse_dates.py b/pandas/tests/io/parser/test_parse_dates.py
index 928cf11650722..1480fc8353f99 100644
--- a/pandas/tests/io/parser/test_parse_dates.py
+++ b/pandas/tests/io/parser/test_parse_dates.py
@@ -802,7 +802,7 @@ def test_parse_dates_custom_euro_format(all_parsers, kwargs):
         tm.assert_frame_equal(df, expected)
     else:
         msg = "got an unexpected keyword argument 'day_first'"
-        with pytest.raises(TypeError, match=msg):
+        with pytest.raises(TypeError, match=msg), pytest.warns(FutureWarning):
             parser.read_csv(
                 StringIO(data),
                 names=["time", "Q", "NTU"],
@@ -1327,12 +1327,13 @@ def test_generic(all_parsers):
     parser = all_parsers
     data = "year,month,day,a\n2001,01,10,10.\n2001,02,1,11."
 
-    result = parser.read_csv(
-        StringIO(data),
-        header=0,
-        parse_dates={"ym": [0, 1]},
-        date_parser=lambda y, m: date(year=int(y), month=int(m), day=1),
-    )
+    with pytest.warns(FutureWarning):
+        result = parser.read_csv(
+            StringIO(data),
+            header=0,
+            parse_dates={"ym": [0, 1]},
+            date_parser=lambda y, m: date(year=int(y), month=int(m), day=1),
+        )
     expected = DataFrame(
         [[date(2001, 1, 1), 10, 10.0], [date(2001, 2, 1), 1, 11.0]],
         columns=["ym", "day", "a"],

From 71297cf999eb0e2b95f399475746bc7ac19aef63 Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Tue, 18 Aug 2020 22:14:50 +0200
Subject: [PATCH 11/19] TST: Update tests for generic_parser in line with
 pandas styleguide

---
 pandas/tests/io/parser/test_parse_dates.py | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/pandas/tests/io/parser/test_parse_dates.py b/pandas/tests/io/parser/test_parse_dates.py
index 1480fc8353f99..d5eae829f67f0 100644
--- a/pandas/tests/io/parser/test_parse_dates.py
+++ b/pandas/tests/io/parser/test_parse_dates.py
@@ -772,6 +772,7 @@ def test_multi_index_parse_dates(all_parsers, index_col):
     tm.assert_frame_equal(result, expected)
 
 
+@pytest.mark.filterwarnings("ignore::FutureWarning")
 @pytest.mark.parametrize("kwargs", [dict(dayfirst=True), dict(day_first=True)])
 def test_parse_dates_custom_euro_format(all_parsers, kwargs):
     parser = all_parsers
@@ -802,7 +803,7 @@ def test_parse_dates_custom_euro_format(all_parsers, kwargs):
         tm.assert_frame_equal(df, expected)
     else:
         msg = "got an unexpected keyword argument 'day_first'"
-        with pytest.raises(TypeError, match=msg), pytest.warns(FutureWarning):
+        with pytest.raises(TypeError, match=msg):
             parser.read_csv(
                 StringIO(data),
                 names=["time", "Q", "NTU"],
@@ -1323,17 +1324,17 @@ def test_datetime_fractional_seconds(all_parsers):
     tm.assert_frame_equal(result, expected)
 
 
+@pytest.mark.filterwarnings("ignore::FutureWarning")
 def test_generic(all_parsers):
     parser = all_parsers
     data = "year,month,day,a\n2001,01,10,10.\n2001,02,1,11."
 
-    with pytest.warns(FutureWarning):
-        result = parser.read_csv(
-            StringIO(data),
-            header=0,
-            parse_dates={"ym": [0, 1]},
-            date_parser=lambda y, m: date(year=int(y), month=int(m), day=1),
-        )
+    result = parser.read_csv(
+        StringIO(data),
+        header=0,
+        parse_dates={"ym": [0, 1]},
+        date_parser=lambda y, m: date(year=int(y), month=int(m), day=1),
+    )
     expected = DataFrame(
         [[date(2001, 1, 1), 10, 10.0], [date(2001, 2, 1), 1, 11.0]],
         columns=["ym", "day", "a"],

From a4a3203adfaeac63d5076783747af3e716a89766 Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Thu, 20 Aug 2020 23:01:00 +0200
Subject: [PATCH 12/19] Assert warnings in test_parse_dates.py instead of
 filtering warnings

---
 pandas/tests/io/parser/test_parse_dates.py | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/pandas/tests/io/parser/test_parse_dates.py b/pandas/tests/io/parser/test_parse_dates.py
index d5eae829f67f0..6b059d01ada6f 100644
--- a/pandas/tests/io/parser/test_parse_dates.py
+++ b/pandas/tests/io/parser/test_parse_dates.py
@@ -772,7 +772,6 @@ def test_multi_index_parse_dates(all_parsers, index_col):
     tm.assert_frame_equal(result, expected)
 
 
-@pytest.mark.filterwarnings("ignore::FutureWarning")
 @pytest.mark.parametrize("kwargs", [dict(dayfirst=True), dict(day_first=True)])
 def test_parse_dates_custom_euro_format(all_parsers, kwargs):
     parser = all_parsers
@@ -803,7 +802,9 @@ def test_parse_dates_custom_euro_format(all_parsers, kwargs):
         tm.assert_frame_equal(df, expected)
     else:
         msg = "got an unexpected keyword argument 'day_first'"
-        with pytest.raises(TypeError, match=msg):
+        with pytest.raises(TypeError, match=msg), tm.assert_produces_warning(
+            FutureWarning
+        ):
             parser.read_csv(
                 StringIO(data),
                 names=["time", "Q", "NTU"],
@@ -1324,17 +1325,17 @@ def test_datetime_fractional_seconds(all_parsers):
     tm.assert_frame_equal(result, expected)
 
 
-@pytest.mark.filterwarnings("ignore::FutureWarning")
 def test_generic(all_parsers):
     parser = all_parsers
     data = "year,month,day,a\n2001,01,10,10.\n2001,02,1,11."
 
-    result = parser.read_csv(
-        StringIO(data),
-        header=0,
-        parse_dates={"ym": [0, 1]},
-        date_parser=lambda y, m: date(year=int(y), month=int(m), day=1),
-    )
+    with tm.assert_produces_warning(FutureWarning, check_stacklevel=False):
+        result = parser.read_csv(
+            StringIO(data),
+            header=0,
+            parse_dates={"ym": [0, 1]},
+            date_parser=lambda y, m: date(year=int(y), month=int(m), day=1),
+        )
     expected = DataFrame(
         [[date(2001, 1, 1), 10, 10.0], [date(2001, 2, 1), 1, 11.0]],
         columns=["ym", "day", "a"],

From 8d970ca7bfd405fc450c6e9bb650259ac245f489 Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Tue, 25 Aug 2020 21:08:43 +0200
Subject: [PATCH 13/19] Update deprecated version and remove double doc string
 text

---
 pandas/io/date_converters.py | 22 ++++------------------
 1 file changed, 4 insertions(+), 18 deletions(-)

diff --git a/pandas/io/date_converters.py b/pandas/io/date_converters.py
index 55777f77e4296..0173e0b8e5264 100644
--- a/pandas/io/date_converters.py
+++ b/pandas/io/date_converters.py
@@ -10,10 +10,7 @@ def parse_date_time(date_col, time_col):
     """
     Parse columns with dates and times into a single datetime column.
 
-    .. deprecated:: 1.1.0
-       Use pd.to_datetime(date_col + " " + time_col) instead to get a Pandas Series.
-       Use pd.to_datetime(date_col + " " + time_col).to_pydatetime() instead to get
-        a Numpy array.
+    .. deprecated:: 1.2
     """
     warnings.warn(
         """
@@ -30,11 +27,7 @@ def parse_date_fields(year_col, month_col, day_col):
     """
     Parse columns with years, months and days into a single date column.
 
-    .. deprecated:: 1.1.0
-        Use pd.to_datetime({"year": year_col, "month": month_col, "day": day_col})
-        instead to get a Pandas Series.
-        Use ser = pd.to_datetime({"year": year_col, "month": month_col, "day": day_col})
-        and np.array([s.to_pydatetime() for s in ser]) instead to get a Numpy array.
+    .. deprecated:: 1.2
     """
     warnings.warn(
         """
@@ -54,13 +47,7 @@ def parse_all_fields(year_col, month_col, day_col, hour_col, minute_col, second_
     """
     Parse columns with datetime information into a single datetime column.
 
-    .. deprecated:: 1.1.0
-        Use pd.to_datetime({"year": year_col, "month": month_col, "day": day_col,
-        "hour": hour_col, "minute": minute_col, second": second_col}) instead to get
-        a Pandas Series.
-        Use ser = pd.to_datetime({"year": year_col, "month": month_col, "day": day_col,
-        "hour": hour_col, "minute": minute_col, second": second_col}) and
-        np.array([s.to_pydatetime() for s in ser]) instead to get a Numpy array.
+    .. deprecated:: 1.2
     """
 
     warnings.warn(
@@ -93,8 +80,7 @@ def generic_parser(parse_func, *cols):
     """
     Use dateparser to parse columns with data information into a single datetime column.
 
-    .. deprecated:: 1.1.0
-        Use pd.to_datetime instead.
+    .. deprecated:: 1.2
     """
 
     warnings.warn(

From 2033dc361687aca5be97bb9dcf06042fce4abf7b Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Tue, 25 Aug 2020 21:26:56 +0200
Subject: [PATCH 14/19] Revert to the old implementation of the date_converters
 function and just deprecate

---
 pandas/core/tools/datetimes.py | 20 +-----------------
 pandas/io/date_converters.py   | 37 ++++++++++++++++++++--------------
 2 files changed, 23 insertions(+), 34 deletions(-)

diff --git a/pandas/core/tools/datetimes.py b/pandas/core/tools/datetimes.py
index 1eb8ee4434d39..0adab143f6052 100644
--- a/pandas/core/tools/datetimes.py
+++ b/pandas/core/tools/datetimes.py
@@ -6,7 +6,6 @@
     TYPE_CHECKING,
     Callable,
     List,
-    MutableMapping,
     Optional,
     Tuple,
     TypeVar,
@@ -60,7 +59,7 @@
 # ---------------------------------------------------------------------
 # types used in annotations
 
-ArrayConvertible = Union[List, Tuple, ArrayLike, "Series", MutableMapping]
+ArrayConvertible = Union[List, Tuple, ArrayLike, "Series"]
 Scalar = Union[int, float, str]
 DatetimeScalar = TypeVar("DatetimeScalar", Scalar, datetime)
 DatetimeScalarOrArrayConvertible = Union[DatetimeScalar, ArrayConvertible]
@@ -585,23 +584,6 @@ def to_datetime(
     ...
 
 
-@overload
-def to_datetime(
-    arg: MutableMapping,
-    errors: str = ...,
-    dayfirst: bool = ...,
-    yearfirst: bool = ...,
-    utc: Optional[bool] = ...,
-    format: Optional[str] = ...,
-    exact: bool = ...,
-    unit: Optional[str] = ...,
-    infer_datetime_format: bool = ...,
-    origin=...,
-    cache: bool = ...,
-) -> "Series":
-    ...
-
-
 @overload
 def to_datetime(
     arg: Union[List, Tuple],
diff --git a/pandas/io/date_converters.py b/pandas/io/date_converters.py
index 0173e0b8e5264..f2cd5834ac90d 100644
--- a/pandas/io/date_converters.py
+++ b/pandas/io/date_converters.py
@@ -3,7 +3,7 @@
 
 import numpy as np
 
-from pandas import to_datetime
+from pandas._libs.tslibs import parsing
 
 
 def parse_date_time(date_col, time_col):
@@ -20,7 +20,9 @@ def parse_date_time(date_col, time_col):
         FutureWarning,
         stacklevel=2,
     )
-    return to_datetime(date_col + " " + time_col).to_pydatetime()
+    date_col = _maybe_cast(date_col)
+    time_col = _maybe_cast(time_col)
+    return parsing.try_parse_date_and_time(date_col, time_col)
 
 
 def parse_date_fields(year_col, month_col, day_col):
@@ -39,8 +41,10 @@ def parse_date_fields(year_col, month_col, day_col):
         stacklevel=2,
     )
 
-    ser = to_datetime({"year": year_col, "month": month_col, "day": day_col})
-    return np.array([s.to_pydatetime() for s in ser])
+    year_col = _maybe_cast(year_col)
+    month_col = _maybe_cast(month_col)
+    day_col = _maybe_cast(day_col)
+    return parsing.try_parse_year_month_day(year_col, month_col, day_col)
 
 
 def parse_all_fields(year_col, month_col, day_col, hour_col, minute_col, second_col):
@@ -62,19 +66,16 @@ def parse_all_fields(year_col, month_col, day_col, hour_col, minute_col, second_
         stacklevel=2,
     )
 
-    ser = to_datetime(
-        {
-            "year": year_col,
-            "month": month_col,
-            "day": day_col,
-            "hour": hour_col,
-            "minute": minute_col,
-            "second": second_col,
-        }
+    year_col = _maybe_cast(year_col)
+    month_col = _maybe_cast(month_col)
+    day_col = _maybe_cast(day_col)
+    hour_col = _maybe_cast(hour_col)
+    minute_col = _maybe_cast(minute_col)
+    second_col = _maybe_cast(second_col)
+    return parsing.try_parse_datetime_components(
+        year_col, month_col, day_col, hour_col, minute_col, second_col
     )
 
-    return np.array([s.to_pydatetime() for s in ser])
-
 
 def generic_parser(parse_func, *cols):
     """
@@ -101,6 +102,12 @@ def generic_parser(parse_func, *cols):
     return results
 
 
+def _maybe_cast(arr):
+    if not arr.dtype.type == np.object_:
+        arr = np.array(arr, dtype=object)
+    return arr
+
+
 def _check_columns(cols):
     if not len(cols):
         raise AssertionError("There must be at least 1 column")

From 8f90441a086f61bf72a9750bca3039ba7693c245 Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Wed, 26 Aug 2020 20:57:11 +0200
Subject: [PATCH 15/19] Remove superfluous noqa statement

---
 pandas/io/date_converters.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/io/date_converters.py b/pandas/io/date_converters.py
index f2cd5834ac90d..f079a25f69fec 100644
--- a/pandas/io/date_converters.py
+++ b/pandas/io/date_converters.py
@@ -87,7 +87,7 @@ def generic_parser(parse_func, *cols):
     warnings.warn(
         """
         Use pd.to_datetime instead.
-""",  # noqa: E501
+""",
         FutureWarning,
         stacklevel=2,
     )

From 2a2a271be5ae708fc5d921cb7c86eb30fbd23418 Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Wed, 26 Aug 2020 21:27:09 +0200
Subject: [PATCH 16/19] Only assert warnings for lines that produce a warning

---
 pandas/tests/io/test_date_converters.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/pandas/tests/io/test_date_converters.py b/pandas/tests/io/test_date_converters.py
index 4fb53decfd887..a9fa27e091714 100644
--- a/pandas/tests/io/test_date_converters.py
+++ b/pandas/tests/io/test_date_converters.py
@@ -14,7 +14,7 @@ def test_parse_date_time():
     expected = np.array([datetime(2007, 1, 3, 5, 7, 9), datetime(2008, 2, 4, 6, 8, 0)])
     with tm.assert_produces_warning(FutureWarning):
         result = conv.parse_date_time(dates, times)
-        tm.assert_numpy_array_equal(result, expected)
+    tm.assert_numpy_array_equal(result, expected)
 
 
 def test_parse_date_fields():
@@ -25,7 +25,7 @@ def test_parse_date_fields():
 
     with tm.assert_produces_warning(FutureWarning):
         result = conv.parse_date_fields(years, months, days)
-        tm.assert_numpy_array_equal(result, expected)
+    tm.assert_numpy_array_equal(result, expected)
 
 
 def test_parse_all_fields():
@@ -40,4 +40,4 @@ def test_parse_all_fields():
 
     with tm.assert_produces_warning(FutureWarning):
         result = conv.parse_all_fields(years, months, days, hours, minutes, seconds)
-        tm.assert_numpy_array_equal(result, expected)
+    tm.assert_numpy_array_equal(result, expected)

From 427bbf0ee666a34dcef44f9a02cf17707501cf85 Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Sat, 29 Aug 2020 15:37:44 +0200
Subject: [PATCH 17/19] Add pytest parametrize to test old and new dateparser
 function

---
 pandas/tests/io/parser/test_parse_dates.py | 105 +++++++++++++++------
 1 file changed, 77 insertions(+), 28 deletions(-)

diff --git a/pandas/tests/io/parser/test_parse_dates.py b/pandas/tests/io/parser/test_parse_dates.py
index 6b059d01ada6f..c349f6b776a6f 100644
--- a/pandas/tests/io/parser/test_parse_dates.py
+++ b/pandas/tests/io/parser/test_parse_dates.py
@@ -23,6 +23,8 @@
 import pandas._testing as tm
 from pandas.core.indexes.datetimes import date_range
 
+import pandas.io.date_converters as conv
+
 # constant
 _DEFAULT_DATETIME = datetime(1, 1, 1)
 
@@ -368,7 +370,11 @@ def test_date_col_as_index_col(all_parsers):
     tm.assert_frame_equal(result, expected)
 
 
-def test_multiple_date_cols_int_cast(all_parsers):
+@pytest.mark.parametrize(
+    "date_parser, warning",
+    ([conv.parse_date_time, FutureWarning], [pd.to_datetime, None]),
+)
+def test_multiple_date_cols_int_cast(all_parsers, date_parser, warning):
     data = (
         "KORD,19990127, 19:00:00, 18:56:00, 0.8100\n"
         "KORD,19990127, 20:00:00, 19:56:00, 0.0100\n"
@@ -380,9 +386,15 @@ def test_multiple_date_cols_int_cast(all_parsers):
     parse_dates = {"actual": [1, 2], "nominal": [1, 3]}
     parser = all_parsers
 
-    result = parser.read_csv(
-        StringIO(data), header=None, parse_dates=parse_dates, prefix="X",
-    )
+    with tm.assert_produces_warning(warning, check_stacklevel=False):
+        result = parser.read_csv(
+            StringIO(data),
+            header=None,
+            date_parser=date_parser,
+            parse_dates=parse_dates,
+            prefix="X",
+        )
+
     expected = DataFrame(
         [
             [datetime(1999, 1, 27, 19, 0), datetime(1999, 1, 27, 18, 56), "KORD", 0.81],
@@ -1162,7 +1174,11 @@ def test_parse_dates_no_convert_thousands(all_parsers, data, kwargs, expected):
     tm.assert_frame_equal(result, expected)
 
 
-def test_parse_date_time_multi_level_column_name(all_parsers):
+@pytest.mark.parametrize(
+    "date_parser, warning",
+    ([conv.parse_date_time, FutureWarning], [pd.to_datetime, None]),
+)
+def test_parse_date_time_multi_level_column_name(all_parsers, date_parser, warning):
     data = """\
 D,T,A,B
 date, time,a,b
@@ -1170,9 +1186,13 @@ def test_parse_date_time_multi_level_column_name(all_parsers):
 2001-01-06, 00:00:00, 1.0, 11.
 """
     parser = all_parsers
-    result = parser.read_csv(
-        StringIO(data), header=[0, 1], parse_dates={"date_time": [0, 1]},
-    )
+    with tm.assert_produces_warning(warning, check_stacklevel=False):
+        result = parser.read_csv(
+            StringIO(data),
+            header=[0, 1],
+            parse_dates={"date_time": [0, 1]},
+            date_parser=date_parser,
+        )
 
     expected_data = [
         [datetime(2001, 1, 5, 9, 0, 0), 0.0, 10.0],
@@ -1182,6 +1202,10 @@ def test_parse_date_time_multi_level_column_name(all_parsers):
     tm.assert_frame_equal(result, expected)
 
 
+@pytest.mark.parametrize(
+    "date_parser, warning",
+    ([conv.parse_date_time, FutureWarning], [pd.to_datetime, None]),
+)
 @pytest.mark.parametrize(
     "data,kwargs,expected",
     [
@@ -1254,9 +1278,10 @@ def test_parse_date_time_multi_level_column_name(all_parsers):
         ),
     ],
 )
-def test_parse_date_time(all_parsers, data, kwargs, expected):
+def test_parse_date_time(all_parsers, data, kwargs, expected, date_parser, warning):
     parser = all_parsers
-    result = parser.read_csv(StringIO(data), **kwargs)
+    with tm.assert_produces_warning(warning, check_stacklevel=False):
+        result = parser.read_csv(StringIO(data), date_parser=date_parser, **kwargs)
 
     # Python can sometimes be flaky about how
     # the aggregated columns are entered, so
@@ -1265,10 +1290,20 @@ def test_parse_date_time(all_parsers, data, kwargs, expected):
     tm.assert_frame_equal(result, expected)
 
 
-def test_parse_date_fields(all_parsers):
+@pytest.mark.parametrize(
+    "date_parser, warning",
+    ([conv.parse_date_fields, FutureWarning], [pd.to_datetime, None]),
+)
+def test_parse_date_fields(all_parsers, date_parser, warning):
     parser = all_parsers
     data = "year,month,day,a\n2001,01,10,10.\n2001,02,1,11."
-    result = parser.read_csv(StringIO(data), header=0, parse_dates={"ymd": [0, 1, 2]},)
+    with tm.assert_produces_warning(warning, check_stacklevel=False):
+        result = parser.read_csv(
+            StringIO(data),
+            header=0,
+            parse_dates={"ymd": [0, 1, 2]},
+            date_parser=date_parser,
+        )
 
     expected = DataFrame(
         [[datetime(2001, 1, 10), 10.0], [datetime(2001, 2, 1), 11.0]],
@@ -1277,20 +1312,27 @@ def test_parse_date_fields(all_parsers):
     tm.assert_frame_equal(result, expected)
 
 
-def test_parse_date_all_fields(all_parsers):
-
+@pytest.mark.parametrize(
+    "date_parser, warning",
+    (
+        [conv.parse_all_fields, FutureWarning],
+        [lambda x: pd.to_datetime(x, format="%Y %m %d %H %M %S"), None],
+    ),
+)
+def test_parse_date_all_fields(all_parsers, date_parser, warning):
     parser = all_parsers
     data = """\
 year,month,day,hour,minute,second,a,b
 2001,01,05,10,00,0,0.0,10.
 2001,01,5,10,0,00,1.,11.
 """
-    result = parser.read_csv(
-        StringIO(data),
-        header=0,
-        date_parser=lambda x: pd.to_datetime(x, format="%Y %m %d %H %M %S"),
-        parse_dates={"ymdHMS": [0, 1, 2, 3, 4, 5]},
-    )
+    with tm.assert_produces_warning(warning, check_stacklevel=False):
+        result = parser.read_csv(
+            StringIO(data),
+            header=0,
+            date_parser=date_parser,
+            parse_dates={"ymdHMS": [0, 1, 2, 3, 4, 5]},
+        )
     expected = DataFrame(
         [
             [datetime(2001, 1, 5, 10, 0, 0), 0.0, 10.0],
@@ -1301,20 +1343,27 @@ def test_parse_date_all_fields(all_parsers):
     tm.assert_frame_equal(result, expected)
 
 
-def test_datetime_fractional_seconds(all_parsers):
+@pytest.mark.parametrize(
+    "date_parser, warning",
+    (
+        [conv.parse_all_fields, FutureWarning],
+        [lambda x: pd.to_datetime(x, format="%Y %m %d %H %M %S.%f"), None],
+    ),
+)
+def test_datetime_fractional_seconds(all_parsers, date_parser, warning):
     parser = all_parsers
     data = """\
 year,month,day,hour,minute,second,a,b
 2001,01,05,10,00,0.123456,0.0,10.
 2001,01,5,10,0,0.500000,1.,11.
 """
-    result = parser.read_csv(
-        StringIO(data),
-        header=0,
-        # date_parser=conv.parse_all_fields,
-        date_parser=lambda x: pd.to_datetime(x, format="%Y %m %d %H %M %S.%f"),
-        parse_dates={"ymdHMS": [0, 1, 2, 3, 4, 5]},
-    )
+    with tm.assert_produces_warning(warning, check_stacklevel=False):
+        result = parser.read_csv(
+            StringIO(data),
+            header=0,
+            date_parser=date_parser,
+            parse_dates={"ymdHMS": [0, 1, 2, 3, 4, 5]},
+        )
     expected = DataFrame(
         [
             [datetime(2001, 1, 5, 10, 0, 0, microsecond=123456), 0.0, 10.0],

From 2d80bdc4422dda927f15df917ff89c4551d032cc Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Sun, 6 Sep 2020 22:42:11 +0200
Subject: [PATCH 18/19] Add whatsnew entry

---
 doc/source/whatsnew/v1.2.0.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/source/whatsnew/v1.2.0.rst b/doc/source/whatsnew/v1.2.0.rst
index d7d2e3cf876ca..6e10ec0cbf528 100644
--- a/doc/source/whatsnew/v1.2.0.rst
+++ b/doc/source/whatsnew/v1.2.0.rst
@@ -195,7 +195,7 @@ Deprecations
 ~~~~~~~~~~~~
 - Deprecated parameter ``inplace`` in :meth:`MultiIndex.set_codes` and :meth:`MultiIndex.set_levels` (:issue:`35626`)
 - Deprecated parameter ``dtype`` in :~meth:`Index.copy` on method all index classes. Use the :meth:`Index.astype` method instead for changing dtype(:issue:`35853`)
--
+- Date parser functions :func:`parse_date_time`, :func:`parse_date_fields`, :func:`parse_all_fields` and :func:`generic_parser` from ``pandas.io.date_converters`` are deprecated and will be removed in a future version; use pandas.to_datetime() instead (GH35741)
 
 .. ---------------------------------------------------------------------------
 

From 1458bc77fb7d873d3e76023123e2e9c003cdf242 Mon Sep 17 00:00:00 2001
From: Avinash Pancham <avinashpancham@outlook.com>
Date: Sat, 12 Sep 2020 15:47:28 +0200
Subject: [PATCH 19/19] Update references in whatsnew message

---
 doc/source/whatsnew/v1.2.0.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/source/whatsnew/v1.2.0.rst b/doc/source/whatsnew/v1.2.0.rst
index 6e10ec0cbf528..553954b466071 100644
--- a/doc/source/whatsnew/v1.2.0.rst
+++ b/doc/source/whatsnew/v1.2.0.rst
@@ -195,7 +195,7 @@ Deprecations
 ~~~~~~~~~~~~
 - Deprecated parameter ``inplace`` in :meth:`MultiIndex.set_codes` and :meth:`MultiIndex.set_levels` (:issue:`35626`)
 - Deprecated parameter ``dtype`` in :~meth:`Index.copy` on method all index classes. Use the :meth:`Index.astype` method instead for changing dtype(:issue:`35853`)
-- Date parser functions :func:`parse_date_time`, :func:`parse_date_fields`, :func:`parse_all_fields` and :func:`generic_parser` from ``pandas.io.date_converters`` are deprecated and will be removed in a future version; use pandas.to_datetime() instead (GH35741)
+- Date parser functions :func:`~pandas.io.date_converters.parse_date_time`, :func:`~pandas.io.date_converters.parse_date_fields`, :func:`~pandas.io.date_converters.parse_all_fields` and :func:`~pandas.io.date_converters.generic_parser` from ``pandas.io.date_converters`` are deprecated and will be removed in a future version; use :func:`to_datetime` instead (:issue:`35741`)
 
 .. ---------------------------------------------------------------------------