Added improvements in to_datetime Error reporting message - incorrect field today/now shown in error (pandas-dev#47860)

* Revert "addressing reviews CL#1"

This reverts commit 69dc2d4.

* Added improvements in to_datetime Error reporting message - incorrect field now/today shown as error

* Added improvements in to_datetime Error reporting message - incorrect field now/today shown as error

* added testcase

* adding position info & updated testcase

* precommit format changes

* addressing review comments

* addressing review comments

* addressing review comments

* addressing review comments

* addressing review comments #2

* addressing review comments

Author: dannyi96

Diff for: pandas/_libs/tslib.pyx

@@ -799,6 +799,7 @@ cdef _array_to_datetime_object(
     # We return an object array and only attempt to parse:
     # 1) NaT or NaT-like values
     # 2) datetime strings, which we return as datetime.datetime
+    # 3) special strings - "now" & "today"
     for i in range(n):
         val = values[i]
         if checknull_with_nat_and_na(val) or PyDateTime_Check(val):
@@ -817,7 +818,8 @@ cdef _array_to_datetime_object(
                                                    yearfirst=yearfirst)
                 pydatetime_to_dt64(oresult[i], &dts)
                 check_dts_bounds(&dts)
-            except (ValueError, OverflowError):
+            except (ValueError, OverflowError) as ex:
+                ex.args = (f"{ex} present at position {i}", )
                 if is_coerce:
                     oresult[i] = <object>NaT
                     continue

Diff for: pandas/_libs/tslibs/parsing.pyx

@@ -298,6 +298,14 @@ def parse_datetime_string(
     if dt is not None:
         return dt
 
+    # Handling special case strings today & now
+    if date_string == "now":
+        dt = datetime.now()
+        return dt
+    elif date_string == "today":
+        dt = datetime.today()
+        return dt
+
     try:
         dt, _ = _parse_dateabbr_string(date_string, _DEFAULT_DATETIME, freq=None)
         return dt

Diff for: pandas/tests/tools/test_to_datetime.py

@@ -2591,6 +2591,13 @@ def test_invalid_origins_tzinfo(self):
         with pytest.raises(ValueError, match="must be tz-naive"):
             to_datetime(1, unit="D", origin=datetime(2000, 1, 1, tzinfo=pytz.utc))
 
+    def test_incorrect_value_exception(self):
+        # GH47495
+        with pytest.raises(
+            ValueError, match="Unknown string format: yesterday present at position 1"
+        ):
+            to_datetime(["today", "yesterday"])
+
     @pytest.mark.parametrize("format", [None, "%Y-%m-%d %H:%M:%S"])
     def test_to_datetime_out_of_bounds_with_format_arg(self, format):
         # see gh-23830