gh-158252: Share the numeric strptime parser

Move numeric field parsing into pytime so the time and datetime modules can use it without importing each other. Keep result construction in the caller and expose the day of year for struct_time construction.

Author: pganssle

Include/internal/pycore_time.h

@@ -317,6 +317,22 @@ extern PyTime_t _PyTimeFraction_Mul(
 extern double _PyTimeFraction_Resolution(
     const _PyTimeFraction *frac);
 
+// Locale-independent numeric strptime parsing.
+// A complete match returns 1; otherwise use Lib/_strptime.py. This function
+// neither allocates nor sets exceptions. The calendar date is validated, but
+// seconds may be 60 or 61: callers must apply their own time validation.
+typedef struct {
+    int year, month, day;
+    int hour, minute, second, fraction;
+    int gmtoff;  // INT_MIN means no offset was supplied.
+    int yday;    // January 1 is day 1.
+} _PyTime_StrptimeFields;
+
+// Export for the '_datetime' shared extension.
+PyAPI_FUNC(int) _PyTime_Strptime(
+    PyObject *string, PyObject *format, _PyTime_StrptimeFields *fields);
+
+
 extern PyStatus _PyTime_Init(struct _Py_time_runtime_state *state);
 
 #ifdef __cplusplus

Modules/_datetimemodule.c

@@ -5846,218 +5846,6 @@ datetime_datetime_utcfromtimestamp_impl(PyTypeObject *type,
     return datetime_from_timestamp(type, _PyTime_gmtime, timestamp, Py_None);
 }
 
-/* Locale-independent strptime parsing for _datetime.
- *
- * Return 1 for a complete numeric match, or 0 to use Lib/_strptime.py.
- * Parsing doesn't allocate or set exceptions. In particular, mismatches may
- * require regex backtracking, so their diagnostics belong to the fallback.
- */
-
-typedef struct {
-    int year, month, day;
-    int hour, minute, second, fraction;
-    int gmtoff;  /* INT_MIN means no offset was supplied. */
-} StrptimeFields;
-
-static int
-strptime_digits(const unsigned char *data, Py_ssize_t length, Py_ssize_t pos,
-                int minimum, int maximum, int *value)
-{
-    int count = 0;
-    *value = 0;
-    while (count < maximum && pos + count < length) {
-        unsigned char c = data[pos + count];
-        if (c < '0' || c > '9') {
-            break;
-        }
-        *value = *value * 10 + c - '0';
-        count++;
-    }
-    return count >= minimum ? count : 0;
-}
-
-static int
-strptime_space(unsigned char c)
-{
-    return c == ' ' || c == '\t' || c == '\n' || c == '\r' ||
-           c == '\f' || c == '\v';
-}
-
-static int
-strptime_offset(const unsigned char *data, Py_ssize_t length, Py_ssize_t pos,
-                StrptimeFields *fields)
-{
-    Py_ssize_t remaining = length - pos;
-    if (remaining == 0) {
-        return 1;
-    }
-    if (remaining == 1 && data[pos] == 'Z') {
-        fields->gmtoff = 0;
-        return 1;
-    }
-    /* Offsets containing seconds or fractions use the Python parser. */
-    if ((remaining != 5 && remaining != 6) ||
-        (data[pos] != '+' && data[pos] != '-')) {
-        return 0;
-    }
-    int hours, minutes;
-    int colon = remaining == 6;
-    if ((colon && data[pos + 3] != ':') ||
-        strptime_digits(data, length, pos + 1, 2, 2, &hours) != 2 ||
-        strptime_digits(data, length, pos + 3 + colon, 2, 2, &minutes) != 2 ||
-        hours > 23 || minutes > 59) {
-        return 0;
-    }
-    fields->gmtoff = (hours * 3600 + minutes * 60) *
-                    (data[pos] == '-' ? -1 : 1);
-    return 1;
-}
-
-static int
-strptime_fields(PyObject *string, PyObject *format, StrptimeFields *fields)
-{
-    /* String subclasses and non-ASCII input retain Python's behavior. */
-    if (!PyUnicode_CheckExact(string) || !PyUnicode_CheckExact(format) ||
-        !PyUnicode_IS_ASCII(string) || !PyUnicode_IS_ASCII(format)) {
-        return 0;
-    }
-    const unsigned char *data = PyUnicode_1BYTE_DATA(string);
-    const unsigned char *fmt = PyUnicode_1BYTE_DATA(format);
-    Py_ssize_t length = PyUnicode_GET_LENGTH(string);
-    Py_ssize_t fmt_length = PyUnicode_GET_LENGTH(format);
-    *fields = (StrptimeFields){1900, 1, 1, 0, 0, 0, 0, INT_MIN};
-    unsigned int seen = 0;
-    Py_ssize_t pos = 0;
-
-    for (Py_ssize_t i = 0; i < fmt_length; i++) {
-        unsigned char c = fmt[i];
-        if (strptime_space(c)) {
-            if (pos == length || !strptime_space(data[pos])) {
-                return 0;
-            }
-            while (i + 1 < fmt_length && strptime_space(fmt[i + 1])) {
-                i++;
-            }
-            do {
-                pos++;
-            } while (pos < length && strptime_space(data[pos]));
-            continue;
-        }
-        if (c != '%') {
-            if (pos == length || data[pos++] != c) {
-                return 0;
-            }
-            continue;
-        }
-        if (++i == fmt_length) {
-            return 0;
-        }
-        c = fmt[i];
-        if (c == '%') {
-            if (pos == length || data[pos++] != '%') {
-                return 0;
-            }
-            continue;
-        }
-
-        /* Reject duplicate groups, aliases, and locale-dependent directives. */
-        const char *directives = "YymdHMSfz";
-        const char *directive = strchr(directives, c);
-        if (directive == NULL || c == '\0') {
-            return 0;
-        }
-        unsigned int bit = 1U << (directive - directives);
-        if (seen & bit) {
-            return 0;
-        }
-        seen |= bit;
-
-        if (c == 'z') {
-            if (i != fmt_length - 1 ||
-                !strptime_offset(data, length, pos, fields)) {
-                return 0;
-            }
-            pos = length;
-            continue;
-        }
-
-        int minimum = 1;
-        int maximum = 2;
-        if (c == 'Y') {
-            minimum = maximum = 4;
-        }
-        else if (c == 'y') {
-            minimum = maximum = 2;
-        }
-        else if (c == 'f') {
-            maximum = 6;
-        }
-        else if ((c == 'd' || c == 'H') && pos < length && data[pos] == ' ') {
-            pos++;
-            maximum = 1;
-        }
-        int value;
-        int count = strptime_digits(data, length, pos, minimum, maximum, &value);
-        if (count == 0) {
-            return 0;
-        }
-        pos += count;
-        switch (c) {
-            case 'Y':
-                fields->year = value;
-                break;
-            case 'y':
-                fields->year = value + (value <= 68 ? 2000 : 1900);
-                break;
-            case 'm':
-                if (value < 1 || value > 12) {
-                    return 0;
-                }
-                fields->month = value;
-                break;
-            case 'd':
-                if (value < 1 || value > 31) {
-                    return 0;
-                }
-                fields->day = value;
-                break;
-            case 'H':
-                if (value > 23) {
-                    return 0;
-                }
-                fields->hour = value;
-                break;
-            case 'M':
-                if (value > 59) {
-                    return 0;
-                }
-                fields->minute = value;
-                break;
-            case 'S':
-                if (value > 61) {
-                    return 0;
-                }
-                fields->second = value;
-                break;
-            case 'f':
-                while (count++ < 6) {
-                    value *= 10;
-                }
-                fields->fraction = value;
-                break;
-        }
-    }
-    /* Mixed %Y/%y and day-without-year diagnostics belong to Python. */
-    if (pos != length || (seen & 3) == 3 ||
-        ((seen & (1U << 3)) && !(seen & 3)) ||
-        fields->year < 1 ||
-        fields->day > days_in_month(fields->year, fields->month)) {
-        return 0;
-    }
-    return 1;
-}
-
-
 /*[clinic input]
 @permit_long_summary
 @classmethod
@@ -6079,9 +5867,9 @@ datetime_datetime_strptime_impl(PyTypeObject *type, PyObject *string,
 /*[clinic end generated code: output=af2c2d024f3203f5 input=ef7807589f1d50e7]*/
 {
     /* Subclasses retain the Python parser's constructor arguments. */
-    StrptimeFields fields;
+    _PyTime_StrptimeFields fields;
     if (type == DATETIME_TYPE(NO_STATE) &&
-        strptime_fields(string, format, &fields)) {
+        _PyTime_Strptime(string, format, &fields)) {
         PyObject *tzinfo = tzinfo_from_isoformat_results(
             fields.gmtoff != INT_MIN, fields.gmtoff, 0);
         if (tzinfo == NULL) {