Reviewer comments; remove cython decorators

Reviewer request to import NaT in parse_time_string

Author: jbrockmendel

pandas/_libs/tslib.pyx

@@ -66,7 +66,6 @@ from khash cimport (
     kh_init_int64, kh_int64_t,
     kh_resize_int64, kh_get_int64)
 
-from tslibs.parsing import parse_time_string as _parse_time_string
 from tslibs import parsing  # noqa
 from tslibs.parsing import ( # noqa
     DateParseError,
@@ -75,6 +74,7 @@ from tslibs.parsing import ( # noqa
     _guess_datetime_format,
     NAT_SENTINEL,
     parse_datetime_string,
+    parse_time_string,
     _does_string_look_like_datetime,
     parse_datetime_string_with_reso)
 
@@ -5454,32 +5454,3 @@ cdef _calc_julian_from_U_or_W(int year, int week_of_year,
 
 # def _strptime_time(data_string, format="%a %b %d %H:%M:%S %Y"):
 #     return _strptime(data_string, format)[0]
-
-#----------------------------------------------------------------------
-# Parsing
-# Wrap tslibs.parsing functions to return `NaT` instead of `NAT_SENTINEL`
-
-
-def parse_time_string(arg, freq=None, dayfirst=None, yearfirst=None):
-    """
-    Try hard to parse datetime string, leveraging dateutil plus some extra
-    goodies like quarter recognition.
-
-    Parameters
-    ----------
-    arg : compat.string_types
-    freq : str or DateOffset, default None
-        Helps with interpreting time string if supplied
-    dayfirst : bool, default None
-        If None uses default from print_config
-    yearfirst : bool, default None
-        If None uses default from print_config
-
-    Returns
-    -------
-    datetime, datetime/dateutil.parser._result, str
-    """
-    res = _parse_time_string(arg, freq, dayfirst, yearfirst)
-    if isinstance(res, tuple) and res[0] is NAT_SENTINEL:
-        res = (NaT,) + res[1:]
-    return res

pandas/_libs/tslibs/parsing.pyx

@@ -107,7 +107,24 @@ def parse_datetime_string(date_string, freq=None, dayfirst=False,
 
 
 def parse_time_string(arg, freq=None, dayfirst=None, yearfirst=None):
-    """See tslib.parse_time_string.__doc__"""    
+    """
+    Try hard to parse datetime string, leveraging dateutil plus some extra
+    goodies like quarter recognition.
+
+    Parameters
+    ----------
+    arg : compat.string_types
+    freq : str or DateOffset, default None
+        Helps with interpreting time string if supplied
+    dayfirst : bool, default None
+        If None uses default from print_config
+    yearfirst : bool, default None
+        If None uses default from print_config
+
+    Returns
+    -------
+    datetime, datetime/dateutil.parser._result, str
+    """
     if not isinstance(arg, string_types):
         return arg
 
@@ -121,9 +138,14 @@ def parse_time_string(arg, freq=None, dayfirst=None, yearfirst=None):
         from pandas.core.config import get_option
         yearfirst = get_option("display.date_yearfirst")
 
-    return parse_datetime_string_with_reso(arg, freq=freq,
-                                                 dayfirst=dayfirst,
-                                                 yearfirst=yearfirst)
+    res = parse_datetime_string_with_reso(arg, freq=freq,
+                                          dayfirst=dayfirst,
+                                          yearfirst=yearfirst)
+    if res[0] is NAT_SENTINEL:
+        from pandas._libs.tslib import NaT
+        res = (NaT,) + res[1:]
+    return res
+
 
 
 def parse_datetime_string_with_reso(date_string, freq=None, dayfirst=False,
@@ -349,10 +371,7 @@ def dateutil_parse(object timestr, object default, ignoretz=False,
 
 
 # The canonical place for this appears to be in frequencies.pyx.
-@cython.returns(object)
-@cython.locals(source=object, default=object)
-@cython.ccall
-def _get_rule_month(source, default='DEC'):
+cpdef object _get_rule_month(object source, object default='DEC'):
     """
     Return starting month of given freq, default is December.