bpo-27268: Fix incorrect error message on float('') (GH-2745)

Python/pystrtod.c

@@ -353,15 +353,15 @@ PyOS_string_to_double(const char *s,
     else if (!endptr && (fail_pos == s || *fail_pos != '\0'))
         PyErr_Format(PyExc_ValueError,
                       "could not convert string to float: "
-                      "%.200s", s);
+                      "'%.200s'", s);
     else if (fail_pos == s)
         PyErr_Format(PyExc_ValueError,
                       "could not convert string to float: "
-                      "%.200s", s);
+                      "'%.200s'", s);
     else if (errno == ERANGE && fabs(x) >= 1.0 && overflow_exception)
         PyErr_Format(overflow_exception,
                       "value too large to convert to float: "
-                      "%.200s", s);
+                      "'%.200s'", s);
     else
         result = x;