PERF: Cython version of Python _TIMEPAT regexp in parsing.pyx (pandas-dev#26204)

Author: anmyachev

asv_bench/benchmarks/io/csv.py

@@ -234,11 +234,12 @@ def mem_parser_chunks(self):
 
 
 class ReadCSVParseSpecialDate(StringIORewind):
-    params = (['mY', 'mdY'],)
+    params = (['mY', 'mdY', 'hm'],)
     params_name = ['value']
     objects = {
         'mY': '01-2019\n10-2019\n02/2000\n',
-        'mdY': '12/02/2010\n'
+        'mdY': '12/02/2010\n',
+        'hm': '21:34\n'
     }
 
     def setup(self, value):

pandas/_libs/tslibs/parsing.pyx

@@ -70,9 +70,8 @@ class DateParseError(ValueError):
 _DEFAULT_DATETIME = datetime(1, 1, 1).replace(hour=0, minute=0,
                                               second=0, microsecond=0)
 
-cdef object _TIMEPAT = re.compile(r'^([01]?[0-9]|2[0-3]):([0-5][0-9])')
-
-cdef set _not_datelike_strings = {'a', 'A', 'm', 'M', 'p', 'P', 't', 'T'}
+cdef:
+    set _not_datelike_strings = {'a', 'A', 'm', 'M', 'p', 'P', 't', 'T'}
 
 # ----------------------------------------------------------------------
 cdef:
@@ -170,6 +169,38 @@ cdef inline object _parse_delimited_date(object date_string, bint dayfirst):
     raise DateParseError("Invalid date specified ({}/{})".format(month, day))
 
 
+cdef inline bint does_string_look_like_time(object parse_string):
+    """
+    Checks whether given string is a time: it has to start either from
+    H:MM or from HH:MM, and hour and minute values must be valid.
+
+    Parameters
+    ----------
+    date_string : str
+
+    Returns:
+    --------
+    whether given string is a time
+    """
+    cdef:
+        const char* buf
+        Py_ssize_t length
+        int hour = -1, minute = -1
+
+    buf = get_c_string_buf_and_size(parse_string, &length)
+    if length >= 4:
+        if buf[1] == b':':
+            # h:MM format
+            hour = getdigit_ascii(buf[0], -1)
+            minute = _parse_2digit(buf + 2)
+        elif buf[2] == b':':
+            # HH:MM format
+            hour = _parse_2digit(buf)
+            minute = _parse_2digit(buf + 3)
+
+    return 0 <= hour <= 23 and 0 <= minute <= 59
+
+
 def parse_datetime_string(date_string, freq=None, dayfirst=False,
                           yearfirst=False, **kwargs):
     """parse datetime string, only returns datetime.
@@ -186,7 +217,7 @@ def parse_datetime_string(date_string, freq=None, dayfirst=False,
     if not _does_string_look_like_datetime(date_string):
         raise ValueError('Given date string not likely a datetime.')
 
-    if _TIMEPAT.match(date_string):
+    if does_string_look_like_time(date_string):
         # use current datetime as default, not pass _DEFAULT_DATETIME
         dt = du_parse(date_string, dayfirst=dayfirst,
                       yearfirst=yearfirst, **kwargs)