Apply Victor's usggestions

Co-authored-by: Victor Stinner <vstinner@python.org>

Author: StanFromIreland

Doc/whatsnew/3.16.rst

@@ -340,6 +340,16 @@ concurrent.futures
   (Contributed by xzmeng and Serhiy Storchaka in :gh:`108518`.)
 
 
+datetime
+--------
+
+* Add the ``%Nf`` format code (where *N* is from 1 to 6) to
+  :meth:`datetime.datetime.strftime`, :meth:`datetime.time.strftime`,
+  :meth:`datetime.date.strftime`, :meth:`datetime.datetime.strptime` and
+  :meth:`datetime.time.strptime`.
+  (Contributed by Stan Ulbrych and Karoline Pauls in :gh:`157290`.)
+
+
 difflib
 -------
 

Lib/_pydatetime.py

@@ -242,7 +242,8 @@ def _wrap_strftime(object, format, timetuple):
                     if freplace is None:
                         freplace = '%06d' % getattr(object,
                                                     'microsecond', 0)
-                    newformat.append(freplace[:int(ch)])
+                    precision = int(ch)
+                    newformat.append(freplace[:precision])
                 elif ch == 'z':
                     if zreplace is None:
                         if hasattr(object, "utcoffset"):

Modules/_datetimemodule.c

@@ -1983,8 +1983,9 @@ wrap_strftime(PyObject *object, PyObject *format, PyObject *timetuple,
                 goto Error;
             }
             start = i;
+            Py_ssize_t precision = ch - '0';
             if (PyUnicodeWriter_WriteSubstring(writer, freplacement,
-                                               0, ch - '0') < 0)
+                                               0, precision) < 0)
             {
                 goto Error;
             }