From 3e986f16c93a6c5be729bce0b5f8efc3c8beb30b Mon Sep 17 00:00:00 2001
From: Brock Mendel <jbrockmendel@gmail.com>
Date: Fri, 17 Nov 2017 20:03:56 -0800
Subject: [PATCH 1/5] centralize remaining uses of
 pandas_datetime_to_datetimestruct in conversion

---
 pandas/_libs/index.pyx                        |  2 +-
 pandas/_libs/tslib.pxd                        |  2 -
 pandas/_libs/tslib.pyx                        | 86 +------------------
 pandas/_libs/tslibs/conversion.pxd            |  2 +
 pandas/_libs/tslibs/conversion.pyx            | 82 +++++++++++++++++-
 pandas/core/indexes/datetimes.py              |  2 +-
 pandas/core/internals.py                      |  7 +-
 pandas/core/tools/datetimes.py                |  4 +-
 .../indexes/datetimes/test_construction.py    |  3 +-
 9 files changed, 95 insertions(+), 95 deletions(-)

diff --git a/pandas/_libs/index.pyx b/pandas/_libs/index.pyx
index d74673b17c8d9..ecb315bca2031 100644
--- a/pandas/_libs/index.pyx
+++ b/pandas/_libs/index.pyx
@@ -13,7 +13,7 @@ cimport util
 
 import numpy as np
 
-from tslib cimport _to_i8
+from tslibs.conversion cimport _to_i8
 
 from hashtable cimport HashTable
 
diff --git a/pandas/_libs/tslib.pxd b/pandas/_libs/tslib.pxd
index 1c2c679904868..c764f486c0b12 100644
--- a/pandas/_libs/tslib.pxd
+++ b/pandas/_libs/tslib.pxd
@@ -3,5 +3,3 @@ from numpy cimport ndarray, int64_t
 from tslibs.conversion cimport convert_to_tsobject
 
 cdef bint _check_all_nulls(obj)
-
-cdef _to_i8(object val)
diff --git a/pandas/_libs/tslib.pyx b/pandas/_libs/tslib.pyx
index 0777b83de4645..bd2bc98deda4f 100644
--- a/pandas/_libs/tslib.pyx
+++ b/pandas/_libs/tslib.pyx
@@ -36,7 +36,7 @@ from cpython.datetime cimport (PyDelta_Check, PyTZInfo_Check,
 # import datetime C API
 PyDateTime_IMPORT
 # this is our datetime.pxd
-from datetime cimport pandas_datetime_to_datetimestruct, _string_to_dts
+from datetime cimport _string_to_dts
 
 # stdlib datetime imports
 from datetime import time as datetime_time
@@ -46,10 +46,9 @@ from tslibs.np_datetime cimport (check_dts_bounds,
                                  reverse_ops,
                                  cmp_scalar,
                                  pandas_datetimestruct,
-                                 PANDAS_DATETIMEUNIT, PANDAS_FR_ns,
                                  dt64_to_dtstruct, dtstruct_to_dt64,
                                  pydatetime_to_dt64, pydate_to_dt64,
-                                 get_datetime64_unit, get_datetime64_value,
+                                 get_datetime64_value,
                                  get_timedelta64_value,
                                  days_per_month_table,
                                  dayofweek, is_leapyear)
@@ -1242,43 +1241,6 @@ cpdef inline object _localize_pydatetime(object dt, object tz):
         return dt.replace(tzinfo=tz)
 
 
-def datetime_to_datetime64(ndarray[object] values):
-    cdef:
-        Py_ssize_t i, n = len(values)
-        object val, inferred_tz = None
-        ndarray[int64_t] iresult
-        pandas_datetimestruct dts
-        _TSObject _ts
-
-    result = np.empty(n, dtype='M8[ns]')
-    iresult = result.view('i8')
-    for i in range(n):
-        val = values[i]
-        if _checknull_with_nat(val):
-            iresult[i] = NPY_NAT
-        elif PyDateTime_Check(val):
-            if val.tzinfo is not None:
-                if inferred_tz is not None:
-                    if get_timezone(val.tzinfo) != inferred_tz:
-                        raise ValueError('Array must be all same time zone')
-                else:
-                    inferred_tz = get_timezone(val.tzinfo)
-
-                _ts = convert_datetime_to_tsobject(val, None)
-                iresult[i] = _ts.value
-                check_dts_bounds(&_ts.dts)
-            else:
-                if inferred_tz is not None:
-                    raise ValueError('Cannot mix tz-aware with '
-                                     'tz-naive values')
-                iresult[i] = pydatetime_to_dt64(val, &dts)
-                check_dts_bounds(&dts)
-        else:
-            raise TypeError('Unrecognized value type: %s' % type(val))
-
-    return result, inferred_tz
-
-
 def format_array_from_datetime(ndarray[int64_t] values, object tz=None,
                                object format=None, object na_rep=None):
     """
@@ -1758,50 +1720,6 @@ cpdef array_to_datetime(ndarray[object] values, errors='raise',
         return oresult
 
 
-# ----------------------------------------------------------------------
-# Conversion routines
-
-def cast_to_nanoseconds(ndarray arr):
-    cdef:
-        Py_ssize_t i, n = arr.size
-        ndarray[int64_t] ivalues, iresult
-        PANDAS_DATETIMEUNIT unit
-        pandas_datetimestruct dts
-
-    shape = (<object> arr).shape
-
-    ivalues = arr.view(np.int64).ravel()
-
-    result = np.empty(shape, dtype='M8[ns]')
-    iresult = result.ravel().view(np.int64)
-
-    if len(iresult) == 0:
-        return result
-
-    unit = get_datetime64_unit(arr.flat[0])
-    for i in range(n):
-        if ivalues[i] != NPY_NAT:
-            pandas_datetime_to_datetimestruct(ivalues[i], unit, &dts)
-            iresult[i] = dtstruct_to_dt64(&dts)
-            check_dts_bounds(&dts)
-        else:
-            iresult[i] = NPY_NAT
-
-    return result
-
-
-cdef inline _to_i8(object val):
-    cdef pandas_datetimestruct dts
-    try:
-        return val.value
-    except AttributeError:
-        if is_datetime64_object(val):
-            return get_datetime64_value(val)
-        elif PyDateTime_Check(val):
-            return Timestamp(val).value
-        return val
-
-
 # ----------------------------------------------------------------------
 # Accessors
 
diff --git a/pandas/_libs/tslibs/conversion.pxd b/pandas/_libs/tslibs/conversion.pxd
index ad817ce8852f2..5b0faa02515dc 100644
--- a/pandas/_libs/tslibs/conversion.pxd
+++ b/pandas/_libs/tslibs/conversion.pxd
@@ -28,3 +28,5 @@ cpdef int64_t tz_convert_single(int64_t val, object tz1, object tz2)
 cdef int64_t get_datetime64_nanos(object val) except? -1
 
 cpdef int64_t pydt_to_i8(object pydt) except? -1
+
+cdef _to_i8(object val)
diff --git a/pandas/_libs/tslibs/conversion.pyx b/pandas/_libs/tslibs/conversion.pyx
index 2a55180b53498..868ec5d12f10d 100644
--- a/pandas/_libs/tslibs/conversion.pyx
+++ b/pandas/_libs/tslibs/conversion.pyx
@@ -40,7 +40,7 @@ from timezones cimport (
 from parsing import parse_datetime_string
 
 from nattype import nat_strings, NaT
-from nattype cimport NPY_NAT
+from nattype cimport NPY_NAT, _checknull_with_nat
 
 # ----------------------------------------------------------------------
 # Constants
@@ -73,6 +73,86 @@ cdef inline int64_t get_datetime64_nanos(object val) except? -1:
 
     return ival
 
+
+def cast_to_nanoseconds(ndarray arr):
+    cdef:
+        Py_ssize_t i, n = arr.size
+        ndarray[int64_t] ivalues, iresult
+        PANDAS_DATETIMEUNIT unit
+        pandas_datetimestruct dts
+
+    shape = (<object> arr).shape
+
+    ivalues = arr.view(np.int64).ravel()
+
+    result = np.empty(shape, dtype='M8[ns]')
+    iresult = result.ravel().view(np.int64)
+
+    if len(iresult) == 0:
+        return result
+
+    unit = get_datetime64_unit(arr.flat[0])
+    for i in range(n):
+        if ivalues[i] != NPY_NAT:
+            pandas_datetime_to_datetimestruct(ivalues[i], unit, &dts)
+            iresult[i] = dtstruct_to_dt64(&dts)
+            check_dts_bounds(&dts)
+        else:
+            iresult[i] = NPY_NAT
+
+    return result
+
+
+def datetime_to_datetime64(ndarray[object] values):
+    cdef:
+        Py_ssize_t i, n = len(values)
+        object val, inferred_tz = None
+        ndarray[int64_t] iresult
+        pandas_datetimestruct dts
+        _TSObject _ts
+
+    result = np.empty(n, dtype='M8[ns]')
+    iresult = result.view('i8')
+    for i in range(n):
+        val = values[i]
+        if _checknull_with_nat(val):
+            iresult[i] = NPY_NAT
+        elif PyDateTime_Check(val):
+            if val.tzinfo is not None:
+                if inferred_tz is not None:
+                    if get_timezone(val.tzinfo) != inferred_tz:
+                        raise ValueError('Array must be all same time zone')
+                else:
+                    inferred_tz = get_timezone(val.tzinfo)
+
+                _ts = convert_datetime_to_tsobject(val, None)
+                iresult[i] = _ts.value
+                check_dts_bounds(&_ts.dts)
+            else:
+                if inferred_tz is not None:
+                    raise ValueError('Cannot mix tz-aware with '
+                                     'tz-naive values')
+                iresult[i] = pydatetime_to_dt64(val, &dts)
+                check_dts_bounds(&dts)
+        else:
+            raise TypeError('Unrecognized value type: %s' % type(val))
+
+    return result, inferred_tz
+
+
+cdef inline _to_i8(object val):
+    cdef:
+        pandas_datetimestruct dts
+    try:
+        return val.value
+    except AttributeError:
+        if is_datetime64_object(val):
+            return get_datetime64_value(val)
+        elif PyDateTime_Check(val):
+            convert_datetime_to_tsobject(val, None).value
+        return val
+
+
 # ----------------------------------------------------------------------
 # _TSObject Conversion
 
diff --git a/pandas/core/indexes/datetimes.py b/pandas/core/indexes/datetimes.py
index ba96979435f81..2c0ef318e7640 100644
--- a/pandas/core/indexes/datetimes.py
+++ b/pandas/core/indexes/datetimes.py
@@ -409,7 +409,7 @@ def __new__(cls, data=None,
                     verify_integrity = False
             else:
                 if data.dtype != _NS_DTYPE:
-                    subarr = libts.cast_to_nanoseconds(data)
+                    subarr = conversion.cast_to_nanoseconds(data)
                 else:
                     subarr = data
         else:
diff --git a/pandas/core/internals.py b/pandas/core/internals.py
index 665f9ff8eb7a0..ae2499bbd7047 100644
--- a/pandas/core/internals.py
+++ b/pandas/core/internals.py
@@ -68,6 +68,7 @@
 from pandas._libs import lib, tslib
 from pandas._libs.tslib import Timedelta
 from pandas._libs.lib import BlockPlacement
+from pandas._libs.tslibs import conversion
 
 from pandas.util._decorators import cache_readonly
 from pandas.util._validators import validate_bool_kwarg
@@ -2462,7 +2463,7 @@ class DatetimeBlock(DatetimeLikeBlockMixin, Block):
 
     def __init__(self, values, placement, fastpath=False, **kwargs):
         if values.dtype != _NS_DTYPE:
-            values = tslib.cast_to_nanoseconds(values)
+            values = conversion.cast_to_nanoseconds(values)
 
         super(DatetimeBlock, self).__init__(values, fastpath=True,
                                             placement=placement, **kwargs)
@@ -2584,7 +2585,7 @@ def set(self, locs, values, check=False):
         """
         if values.dtype != _NS_DTYPE:
             # Workaround for numpy 1.6 bug
-            values = tslib.cast_to_nanoseconds(values)
+            values = conversion.cast_to_nanoseconds(values)
 
         self.values[locs] = values
 
@@ -4674,7 +4675,7 @@ def form_blocks(arrays, names, axes):
             complex_items.append((i, k, v))
         elif issubclass(v.dtype.type, np.datetime64):
             if v.dtype != _NS_DTYPE:
-                v = tslib.cast_to_nanoseconds(v)
+                v = conversion.cast_to_nanoseconds(v)
 
             if is_datetimetz(v):
                 datetime_tz_items.append((i, k, v))
diff --git a/pandas/core/tools/datetimes.py b/pandas/core/tools/datetimes.py
index cbf393046907f..65f4704da3800 100644
--- a/pandas/core/tools/datetimes.py
+++ b/pandas/core/tools/datetimes.py
@@ -4,7 +4,7 @@
 
 from pandas._libs import tslib
 from pandas._libs.tslibs.strptime import array_strptime
-from pandas._libs.tslibs import parsing
+from pandas._libs.tslibs import parsing, conversion
 from pandas._libs.tslibs.parsing import (  # noqa
     parse_time_string,
     DateParseError,
@@ -373,7 +373,7 @@ def _convert_listlike(arg, box, format, name=None, tz=tz):
 
         except ValueError as e:
             try:
-                values, tz = tslib.datetime_to_datetime64(arg)
+                values, tz = conversion.datetime_to_datetime64(arg)
                 return DatetimeIndex._simple_new(values, name=name, tz=tz)
             except (ValueError, TypeError):
                 raise e
diff --git a/pandas/tests/indexes/datetimes/test_construction.py b/pandas/tests/indexes/datetimes/test_construction.py
index a4706dd8a3767..388b4c606b9e3 100644
--- a/pandas/tests/indexes/datetimes/test_construction.py
+++ b/pandas/tests/indexes/datetimes/test_construction.py
@@ -9,6 +9,7 @@
 import pandas.util.testing as tm
 from pandas._libs import tslib, lib
 from pandas._libs.tslib import OutOfBoundsDatetime
+from pandas._libs.tslibs import conversion
 from pandas import (DatetimeIndex, Index, Timestamp, datetime, date_range,
                     to_datetime)
 
@@ -496,7 +497,7 @@ def test_index_cast_datetime64_other_units(self):
         arr = np.arange(0, 100, 10, dtype=np.int64).view('M8[D]')
         idx = Index(arr)
 
-        assert (idx.values == tslib.cast_to_nanoseconds(arr)).all()
+        assert (idx.values == conversion.cast_to_nanoseconds(arr)).all()
 
     def test_constructor_int64_nocopy(self):
         # #1624

From 08236be405a1dcda30b524727867b46e077505d4 Mon Sep 17 00:00:00 2001
From: Brock Mendel <jbrockmendel@gmail.com>
Date: Sat, 18 Nov 2017 08:41:25 -0800
Subject: [PATCH 2/5] fixup missing return

---
 pandas/_libs/tslibs/conversion.pyx | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/_libs/tslibs/conversion.pyx b/pandas/_libs/tslibs/conversion.pyx
index 868ec5d12f10d..31fc1900bb8d4 100644
--- a/pandas/_libs/tslibs/conversion.pyx
+++ b/pandas/_libs/tslibs/conversion.pyx
@@ -149,7 +149,7 @@ cdef inline _to_i8(object val):
         if is_datetime64_object(val):
             return get_datetime64_value(val)
         elif PyDateTime_Check(val):
-            convert_datetime_to_tsobject(val, None).value
+            return convert_datetime_to_tsobject(val, None).value
         return val
 
 

From f19eebadf54864f16c2871d2f6e3f577f11ed668 Mon Sep 17 00:00:00 2001
From: Brock Mendel <jbrockmendel@gmail.com>
Date: Sat, 18 Nov 2017 12:10:51 -0800
Subject: [PATCH 3/5] flake8 fixup

---
 pandas/tests/indexes/datetimes/test_construction.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/tests/indexes/datetimes/test_construction.py b/pandas/tests/indexes/datetimes/test_construction.py
index 388b4c606b9e3..1fc1600f432c4 100644
--- a/pandas/tests/indexes/datetimes/test_construction.py
+++ b/pandas/tests/indexes/datetimes/test_construction.py
@@ -7,7 +7,7 @@
 import pandas as pd
 from pandas import offsets
 import pandas.util.testing as tm
-from pandas._libs import tslib, lib
+from pandas._libs import lib
 from pandas._libs.tslib import OutOfBoundsDatetime
 from pandas._libs.tslibs import conversion
 from pandas import (DatetimeIndex, Index, Timestamp, datetime, date_range,

From e156b3f8d8df57afb45f15d29557d8ce99724fc6 Mon Sep 17 00:00:00 2001
From: Brock Mendel <jbrockmendel@gmail.com>
Date: Sat, 18 Nov 2017 17:21:46 -0800
Subject: [PATCH 4/5] docstrings, rename per reviewer request

---
 pandas/_libs/index.pyx             | 14 +++++------
 pandas/_libs/tslibs/conversion.pxd |  2 +-
 pandas/_libs/tslibs/conversion.pyx | 39 +++++++++++++++++++++++++++++-
 3 files changed, 46 insertions(+), 9 deletions(-)

diff --git a/pandas/_libs/index.pyx b/pandas/_libs/index.pyx
index ecb315bca2031..c7178c93139d4 100644
--- a/pandas/_libs/index.pyx
+++ b/pandas/_libs/index.pyx
@@ -13,7 +13,7 @@ cimport util
 
 import numpy as np
 
-from tslibs.conversion cimport _to_i8
+from tslibs.conversion cimport _maybe_datetimelike_to_i8
 
 from hashtable cimport HashTable
 
@@ -405,12 +405,12 @@ cdef class DatetimeEngine(Int64Engine):
             if not self.is_unique:
                 return self._get_loc_duplicates(val)
             values = self._get_index_values()
-            conv = _to_i8(val)
+            conv = _maybe_datetimelike_to_i8(val)
             loc = values.searchsorted(conv, side='left')
             return util.get_value_at(values, loc) == conv
 
         self._ensure_mapping_populated()
-        return _to_i8(val) in self.mapping
+        return _maybe_datetimelike_to_i8(val) in self.mapping
 
     cdef _get_index_values(self):
         return self.vgetter().view('i8')
@@ -425,12 +425,12 @@ cdef class DatetimeEngine(Int64Engine):
         # Welcome to the spaghetti factory
         if self.over_size_threshold and self.is_monotonic_increasing:
             if not self.is_unique:
-                val = _to_i8(val)
+                val = _maybe_datetimelike_to_i8(val)
                 return self._get_loc_duplicates(val)
             values = self._get_index_values()
 
             try:
-                conv = _to_i8(val)
+                conv = _maybe_datetimelike_to_i8(val)
                 loc = values.searchsorted(conv, side='left')
             except TypeError:
                 self._date_check_type(val)
@@ -442,7 +442,7 @@ cdef class DatetimeEngine(Int64Engine):
 
         self._ensure_mapping_populated()
         if not self.unique:
-            val = _to_i8(val)
+            val = _maybe_datetimelike_to_i8(val)
             return self._get_loc_duplicates(val)
 
         try:
@@ -453,7 +453,7 @@ cdef class DatetimeEngine(Int64Engine):
             pass
 
         try:
-            val = _to_i8(val)
+            val = _maybe_datetimelike_to_i8(val)
             return self.mapping.get_item(val)
         except (TypeError, ValueError):
             self._date_check_type(val)
diff --git a/pandas/_libs/tslibs/conversion.pxd b/pandas/_libs/tslibs/conversion.pxd
index 5b0faa02515dc..bf48c98e17298 100644
--- a/pandas/_libs/tslibs/conversion.pxd
+++ b/pandas/_libs/tslibs/conversion.pxd
@@ -29,4 +29,4 @@ cdef int64_t get_datetime64_nanos(object val) except? -1
 
 cpdef int64_t pydt_to_i8(object pydt) except? -1
 
-cdef _to_i8(object val)
+cdef _maybe_datetimelike_to_i8(object val)
diff --git a/pandas/_libs/tslibs/conversion.pyx b/pandas/_libs/tslibs/conversion.pyx
index 31fc1900bb8d4..d925433e0df8d 100644
--- a/pandas/_libs/tslibs/conversion.pyx
+++ b/pandas/_libs/tslibs/conversion.pyx
@@ -75,6 +75,18 @@ cdef inline int64_t get_datetime64_nanos(object val) except? -1:
 
 
 def cast_to_nanoseconds(ndarray arr):
+    """
+    Ensure a np.datetime64 array has dtype specifically 'datetime64[ns]'
+
+    Parameters
+    ----------
+    arr : ndarray
+
+    Returns
+    -------
+    result : ndarray with dtype datetime64[ns]
+
+    """
     cdef:
         Py_ssize_t i, n = arr.size
         ndarray[int64_t] ivalues, iresult
@@ -104,6 +116,19 @@ def cast_to_nanoseconds(ndarray arr):
 
 
 def datetime_to_datetime64(ndarray[object] values):
+    """
+    Convert ndarray of datetime-like objects to int64 array representing
+    nanosecond timestamps.
+
+    Parameters
+    ----------
+    values : ndarray
+
+    Returns
+    -------
+    result : ndarray witth dtype int64
+    inferred_tz : tzinfo or None
+    """
     cdef:
         Py_ssize_t i, n = len(values)
         object val, inferred_tz = None
@@ -140,7 +165,19 @@ def datetime_to_datetime64(ndarray[object] values):
     return result, inferred_tz
 
 
-cdef inline _to_i8(object val):
+cdef inline _maybe_datetimelike_to_i8(object val):
+    """
+    Try to convert to a nanosecond timestamp.  Fall back to returning the
+    input value.
+
+    Parameters
+    ----------
+    val : object
+
+    Returns
+    -------
+    val : int64 timestamp or original input
+    """
     cdef:
         pandas_datetimestruct dts
     try:

From 0ef759f2d9a55eba8099467665dd689d57f95c36 Mon Sep 17 00:00:00 2001
From: Brock Mendel <jbrockmendel@gmail.com>
Date: Sun, 19 Nov 2017 10:02:10 -0800
Subject: [PATCH 5/5] rename per reviewer request, fix typo

---
 pandas/_libs/index.pyx                             | 14 +++++++-------
 pandas/_libs/tslibs/conversion.pxd                 |  2 +-
 pandas/_libs/tslibs/conversion.pyx                 |  6 +++---
 pandas/core/indexes/datetimes.py                   |  2 +-
 pandas/core/internals.py                           |  6 +++---
 .../tests/indexes/datetimes/test_construction.py   |  2 +-
 6 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/pandas/_libs/index.pyx b/pandas/_libs/index.pyx
index c7178c93139d4..e4c188b28bb6e 100644
--- a/pandas/_libs/index.pyx
+++ b/pandas/_libs/index.pyx
@@ -13,7 +13,7 @@ cimport util
 
 import numpy as np
 
-from tslibs.conversion cimport _maybe_datetimelike_to_i8
+from tslibs.conversion cimport maybe_datetimelike_to_i8
 
 from hashtable cimport HashTable
 
@@ -405,12 +405,12 @@ cdef class DatetimeEngine(Int64Engine):
             if not self.is_unique:
                 return self._get_loc_duplicates(val)
             values = self._get_index_values()
-            conv = _maybe_datetimelike_to_i8(val)
+            conv = maybe_datetimelike_to_i8(val)
             loc = values.searchsorted(conv, side='left')
             return util.get_value_at(values, loc) == conv
 
         self._ensure_mapping_populated()
-        return _maybe_datetimelike_to_i8(val) in self.mapping
+        return maybe_datetimelike_to_i8(val) in self.mapping
 
     cdef _get_index_values(self):
         return self.vgetter().view('i8')
@@ -425,12 +425,12 @@ cdef class DatetimeEngine(Int64Engine):
         # Welcome to the spaghetti factory
         if self.over_size_threshold and self.is_monotonic_increasing:
             if not self.is_unique:
-                val = _maybe_datetimelike_to_i8(val)
+                val = maybe_datetimelike_to_i8(val)
                 return self._get_loc_duplicates(val)
             values = self._get_index_values()
 
             try:
-                conv = _maybe_datetimelike_to_i8(val)
+                conv = maybe_datetimelike_to_i8(val)
                 loc = values.searchsorted(conv, side='left')
             except TypeError:
                 self._date_check_type(val)
@@ -442,7 +442,7 @@ cdef class DatetimeEngine(Int64Engine):
 
         self._ensure_mapping_populated()
         if not self.unique:
-            val = _maybe_datetimelike_to_i8(val)
+            val = maybe_datetimelike_to_i8(val)
             return self._get_loc_duplicates(val)
 
         try:
@@ -453,7 +453,7 @@ cdef class DatetimeEngine(Int64Engine):
             pass
 
         try:
-            val = _maybe_datetimelike_to_i8(val)
+            val = maybe_datetimelike_to_i8(val)
             return self.mapping.get_item(val)
         except (TypeError, ValueError):
             self._date_check_type(val)
diff --git a/pandas/_libs/tslibs/conversion.pxd b/pandas/_libs/tslibs/conversion.pxd
index bf48c98e17298..6e7df10e7c424 100644
--- a/pandas/_libs/tslibs/conversion.pxd
+++ b/pandas/_libs/tslibs/conversion.pxd
@@ -29,4 +29,4 @@ cdef int64_t get_datetime64_nanos(object val) except? -1
 
 cpdef int64_t pydt_to_i8(object pydt) except? -1
 
-cdef _maybe_datetimelike_to_i8(object val)
+cdef maybe_datetimelike_to_i8(object val)
diff --git a/pandas/_libs/tslibs/conversion.pyx b/pandas/_libs/tslibs/conversion.pyx
index d925433e0df8d..16e88bcaeea3e 100644
--- a/pandas/_libs/tslibs/conversion.pyx
+++ b/pandas/_libs/tslibs/conversion.pyx
@@ -74,7 +74,7 @@ cdef inline int64_t get_datetime64_nanos(object val) except? -1:
     return ival
 
 
-def cast_to_nanoseconds(ndarray arr):
+def ensure_datetime64ns(ndarray arr):
     """
     Ensure a np.datetime64 array has dtype specifically 'datetime64[ns]'
 
@@ -126,7 +126,7 @@ def datetime_to_datetime64(ndarray[object] values):
 
     Returns
     -------
-    result : ndarray witth dtype int64
+    result : ndarray with dtype int64
     inferred_tz : tzinfo or None
     """
     cdef:
@@ -165,7 +165,7 @@ def datetime_to_datetime64(ndarray[object] values):
     return result, inferred_tz
 
 
-cdef inline _maybe_datetimelike_to_i8(object val):
+cdef inline maybe_datetimelike_to_i8(object val):
     """
     Try to convert to a nanosecond timestamp.  Fall back to returning the
     input value.
diff --git a/pandas/core/indexes/datetimes.py b/pandas/core/indexes/datetimes.py
index 2c0ef318e7640..64b5b9f958880 100644
--- a/pandas/core/indexes/datetimes.py
+++ b/pandas/core/indexes/datetimes.py
@@ -409,7 +409,7 @@ def __new__(cls, data=None,
                     verify_integrity = False
             else:
                 if data.dtype != _NS_DTYPE:
-                    subarr = conversion.cast_to_nanoseconds(data)
+                    subarr = conversion.ensure_datetime64ns(data)
                 else:
                     subarr = data
         else:
diff --git a/pandas/core/internals.py b/pandas/core/internals.py
index ae2499bbd7047..c5b38851f51fd 100644
--- a/pandas/core/internals.py
+++ b/pandas/core/internals.py
@@ -2463,7 +2463,7 @@ class DatetimeBlock(DatetimeLikeBlockMixin, Block):
 
     def __init__(self, values, placement, fastpath=False, **kwargs):
         if values.dtype != _NS_DTYPE:
-            values = conversion.cast_to_nanoseconds(values)
+            values = conversion.ensure_datetime64ns(values)
 
         super(DatetimeBlock, self).__init__(values, fastpath=True,
                                             placement=placement, **kwargs)
@@ -2585,7 +2585,7 @@ def set(self, locs, values, check=False):
         """
         if values.dtype != _NS_DTYPE:
             # Workaround for numpy 1.6 bug
-            values = conversion.cast_to_nanoseconds(values)
+            values = conversion.ensure_datetime64ns(values)
 
         self.values[locs] = values
 
@@ -4675,7 +4675,7 @@ def form_blocks(arrays, names, axes):
             complex_items.append((i, k, v))
         elif issubclass(v.dtype.type, np.datetime64):
             if v.dtype != _NS_DTYPE:
-                v = conversion.cast_to_nanoseconds(v)
+                v = conversion.ensure_datetime64ns(v)
 
             if is_datetimetz(v):
                 datetime_tz_items.append((i, k, v))
diff --git a/pandas/tests/indexes/datetimes/test_construction.py b/pandas/tests/indexes/datetimes/test_construction.py
index 1fc1600f432c4..b59dd25ead57f 100644
--- a/pandas/tests/indexes/datetimes/test_construction.py
+++ b/pandas/tests/indexes/datetimes/test_construction.py
@@ -497,7 +497,7 @@ def test_index_cast_datetime64_other_units(self):
         arr = np.arange(0, 100, 10, dtype=np.int64).view('M8[D]')
         idx = Index(arr)
 
-        assert (idx.values == conversion.cast_to_nanoseconds(arr)).all()
+        assert (idx.values == conversion.ensure_datetime64ns(arr)).all()
 
     def test_constructor_int64_nocopy(self):
         # #1624