implemented _does_string_look_like_datetime in cython

Author: anmyachev

pandas/_libs/tslibs/parsing.pyx

@@ -7,6 +7,7 @@ import re
 import time
 
 from cpython.datetime cimport datetime
+from cpython cimport PyUnicode_Check, PyBytes_Check, PyBytes_AsStringAndSize
 
 
 import numpy as np
@@ -33,7 +34,23 @@ from dateutil.parser import parse as du_parse
 from pandas._libs.tslibs.ccalendar import MONTH_NUMBERS
 from pandas._libs.tslibs.nattype import nat_strings, NaT
 
-from pandas._libs.datehelpers import _does_string_look_like_datetime
+cdef extern from "errno.h":
+    int errno
+
+cdef extern from "../src/parser/tokenizer.h":
+    double xstrtod(const char *p, char **q, char decimal, char sci, char tsep,
+                   int skip_trailing)
+
+cdef extern from *:
+    char* PyUnicode_AsUTF8AndSize(object unicode, Py_ssize_t* length)
+
+cdef inline bint get_string_data(object s, char **buf, Py_ssize_t *length):
+    if PyUnicode_Check(s):
+        buf[0] = PyUnicode_AsUTF8AndSize(s, length)
+        return buf[0] != NULL
+    if PyBytes_Check(s):
+        return PyBytes_AsStringAndSize(s, buf, length) == 0
+    return False
 
 # ----------------------------------------------------------------------
 # Constants
@@ -49,6 +66,8 @@ _DEFAULT_DATETIME = datetime(1, 1, 1).replace(hour=0, minute=0,
 cdef:
     object _TIMEPAT = re.compile(r'^([01]?[0-9]|2[0-3]):([0-5][0-9])')
 
+    set _not_datelike_strings = {'a', 'A', 'm', 'M', 'p', 'P', 't', 'T'}
+
 # ----------------------------------------------------------------------
 
 _get_option = None
@@ -187,6 +206,30 @@ cdef parse_datetime_string_with_reso(date_string, freq=None, dayfirst=False,
     return parsed, parsed, reso
 
 
+cpdef bint _does_string_look_like_datetime(object date_string):
+    cdef:
+        char *buf = NULL
+        char *endptr = NULL
+        Py_ssize_t length = -1
+        double converted_date
+        char first
+
+    if not get_string_data(date_string, &buf, &length):
+        return False
+    if length >= 1:
+        first = buf[0]
+        if first == '0':
+            return True
+        elif length == 1 and date_string in _not_datelike_strings:
+            return False
+        else:
+            converted_date = xstrtod(buf, &endptr, '.', 'e', '\0', 1)
+            if errno == 0 and endptr == buf + length:
+                return converted_date >= 1000
+
+    return True
+
+
 cdef inline object _parse_dateabbr_string(object date_string, object default,
                                           object freq):
     cdef:

pandas/_libs/tslibs/src/datetime/datehelpers.c

@@ -322,75 +322,13 @@ static PyObject* concat_date_cols(PyObject *self, PyObject *args,
     }
 }
 
-static char not_datelike[sizeof(char) * 256];
-
-static PyObject* _does_string_look_like_datetime(PyObject* unused,
-                                                 PyObject* arg) {
-    char *buf = NULL, *endptr = NULL;
-    Py_ssize_t length = -1;
-    double converted_date;
-    int error = 0;
-    int result = 1;
-
-#if PY_MAJOR_VERSION == 2
-    if (!PyString_CheckExact(arg)) {
-        if (!PyUnicode_CheckExact(arg)) {
-            // arg is not a string, so it's certainly
-            // not a datetime-looking string
-            PyErr_SetString(PyExc_ValueError,
-                            "_does_string_look_like_datetime expects a string");
-            return NULL;
-        }
-        buf = PyUnicode_AS_DATA(arg);
-        length = (int)PyUnicode_GET_SIZE(arg);
-    } else {
-        if (PyString_AsStringAndSize(arg, &buf, &length) == -1) {
-            return NULL;
-        }
-    }
-#else
-    if (!PyUnicode_CheckExact(arg) || !PyUnicode_IS_READY(arg)) {
-        PyErr_SetString(PyExc_ValueError,
-                        "_does_string_look_like_datetime expects a string");
-        return NULL;
-    }
-    buf = PyUnicode_DATA(arg);
-    length = PyUnicode_GET_LENGTH(arg);
-#endif
-
-    if (length >= 1) {
-        char first = *buf;
-        if (first == '0') {
-            result = 1;
-        } else if (length == 1 && not_datelike[Py_CHARMASK(first)]) {
-            result = 0;
-        } else {
-            converted_date = xstrtod(buf, &endptr, '.', 'e', '\0', 1);
-            if ((errno == 0) && (endptr == buf + length)) {
-                result = (converted_date >= 1000) ? 1 : 0;
-            }
-        }
-    }
-
-    if (result) {
-        Py_RETURN_TRUE;
-    } else {
-        Py_RETURN_FALSE;
-    }
-}
-
 static PyMethodDef module_methods[] = {
     /* name from python, name in C-file, ..., __doc__ string of method */
     {
         "concat_date_cols", (PyCFunction)concat_date_cols,
         METH_VARARGS | METH_KEYWORDS,
         "concatenates date cols and returns numpy array"
     },
-    {
-        "_does_string_look_like_datetime", _does_string_look_like_datetime,
-        METH_O,
-        "checks if string looks like a datetime"
-    },
     {NULL, NULL, 0, NULL}
 };
 
@@ -418,11 +356,5 @@ PY_DATEHELPERS_MODULE_INIT {
 
     module = PY_MODULE_CREATE;
 
-    memset(not_datelike, 0, sizeof(not_datelike));
-    not_datelike['a'] = not_datelike['A'] = 1;
-    not_datelike['m'] = not_datelike['M'] = 1;
-    not_datelike['p'] = not_datelike['P'] = 1;
-    not_datelike['t'] = not_datelike['T'] = 1;
-
     PY_RETURN_MODULE;
 }

setup.py

@@ -611,7 +611,9 @@ def srcpath(name=None, suffix='.pyx', subdir='src'):
         'sources': np_datetime_sources},
     '_libs.tslibs.parsing': {
         'pyxfile': '_libs/tslibs/parsing',
-        'include': []},
+        'include': common_include,
+        'depends': ['pandas/_libs/src/parser/tokenizer.h'],
+        'sources': ['pandas/_libs/src/parser/tokenizer.c']},
     '_libs.tslibs.period': {
         'pyxfile': '_libs/tslibs/period',
         'include': ts_include,