[utils] Add `datetime_from_str` to parse relative time (#221)

and `datetime_add_months` to accurately add/subtract months

Authored by: colethedj

1 files changed, 13 insertions, 2 deletions

diff --git a/test/test_utils.py b/test/test_utils.py
index 795d2b46a..d0571c6f2 100644
--- a/test/test_utils.py
+++ b/test/test_utils.py
@@ -23,6 +23,7 @@ from yt_dlp.utils import (
     clean_html,
     clean_podcast_url,
     date_from_str,
+    datetime_from_str,
     DateRange,
     detect_exe_version,
     determine_ext,
@@ -311,8 +312,18 @@ class TestUtil(unittest.TestCase):
         self.assertEqual(date_from_str('yesterday'), date_from_str('now-1day'))
         self.assertEqual(date_from_str('now+7day'), date_from_str('now+1week'))
         self.assertEqual(date_from_str('now+14day'), date_from_str('now+2week'))
-        self.assertEqual(date_from_str('now+365day'), date_from_str('now+1year'))
-        self.assertEqual(date_from_str('now+30day'), date_from_str('now+1month'))
+        self.assertEqual(date_from_str('20200229+365day'), date_from_str('20200229+1year'))
+        self.assertEqual(date_from_str('20210131+28day'), date_from_str('20210131+1month'))
+
+    def test_datetime_from_str(self):
+        self.assertEqual(datetime_from_str('yesterday', precision='day'), datetime_from_str('now-1day', precision='auto'))
+        self.assertEqual(datetime_from_str('now+7day', precision='day'), datetime_from_str('now+1week', precision='auto'))
+        self.assertEqual(datetime_from_str('now+14day', precision='day'), datetime_from_str('now+2week', precision='auto'))
+        self.assertEqual(datetime_from_str('20200229+365day', precision='day'), datetime_from_str('20200229+1year', precision='auto'))
+        self.assertEqual(datetime_from_str('20210131+28day', precision='day'), datetime_from_str('20210131+1month', precision='auto'))
+        self.assertEqual(datetime_from_str('20210131+59day', precision='day'), datetime_from_str('20210131+2month', precision='auto'))
+        self.assertEqual(datetime_from_str('now+1day', precision='hour'), datetime_from_str('now+24hours', precision='auto'))
+        self.assertEqual(datetime_from_str('now+23hours', precision='hour'), datetime_from_str('now+23hours', precision='auto'))
 
     def test_daterange(self):
         _20century = DateRange("19000101", "20000101")