[dt] introduce 'NullDatetime' to represent invalid datetimes

gallery_dl/dt.py

@@ -12,6 +12,14 @@ import sys
 import time
 from datetime import datetime, date, timedelta, timezone  # noqa F401
 
+
+class NullDatetime(datetime):
+
+    def __bool__(self):
+        return False
+
+
+NONE = NullDatetime(101, 1, 1)
 EPOCH = datetime(1970, 1, 1)
 SECOND = timedelta(0, 1)
 
@@ -29,7 +37,7 @@ def normalize(dt):
 def convert(value):
     """Convert 'value' to a naive UTC datetime object"""
     if not value:
-        return EPOCH
+        return NONE
 
     if isinstance(value, datetime):
         return value
@@ -51,7 +59,7 @@ def parse(dt_string, format):
     try:
         return normalize(datetime.strptime(dt_string, format))
     except Exception:
-        return EPOCH
+        return NONE
 
 
 if sys.hexversion < 0x30c0000:
@@ -64,7 +72,7 @@ if sys.hexversion < 0x30c0000:
                 dt_string = dt_string[:-1]
             return normalize(datetime.fromisoformat(dt_string))
         except Exception:
-            return EPOCH
+            return NONE
 
     def parse_compat(dt_string, format):
         """Parse 'dt_string' as ISO 8601 value using 'format'"""
@@ -80,7 +88,7 @@ else:
         try:
             return normalize(datetime.fromisoformat(dt_string))
         except Exception:
-            return EPOCH
+            return NONE
 
     def parse_compat(dt_string, format):
         """Parse 'dt_string' as ISO 8601 value"""
@@ -94,7 +102,7 @@ else:
     now = from_ts
 
 
-def parse_ts(ts, default=EPOCH):
+def parse_ts(ts, default=NONE):
     """Create a datetime object from a Unix timestamp"""
     try:
         return from_ts(int(ts))

test/test_dt.py

@@ -44,14 +44,14 @@ class TestDatetime(unittest.TestCase):
         _assert("2010-01-01T00:00:00Z"            , d)
         _assert("2010-01-01T00:00:00.123456Z"     , d)
 
-        _assert(0    , dt.EPOCH)
-        _assert(""   , dt.EPOCH)
-        _assert("foo", dt.EPOCH)
-        _assert(None , dt.EPOCH)
-        _assert(()   , dt.EPOCH)
-        _assert([]   , dt.EPOCH)
-        _assert({}   , dt.EPOCH)
-        _assert((1, 2, 3), dt.EPOCH)
+        _assert(0    , dt.NONE)
+        _assert(""   , dt.NONE)
+        _assert("foo", dt.NONE)
+        _assert(None , dt.NONE)
+        _assert(()   , dt.NONE)
+        _assert([]   , dt.NONE)
+        _assert({}   , dt.NONE)
+        _assert((1, 2, 3), dt.NONE)
 
     @unittest.skipIf(sys.hexversion < 0x30b0000,
                      "extended fromisoformat timezones")
@@ -101,7 +101,7 @@ class TestDatetime(unittest.TestCase):
         self.assertEqual(f("1555816235"), value)
 
         for value in ((), [], {}, None, ""):
-            self.assertEqual(f(value), dt.EPOCH)
+            self.assertEqual(f(value), dt.NONE)
             self.assertEqual(f(value, "foo"), "foo")
 
     def test_parse(self, f=dt.parse):
@@ -119,7 +119,7 @@ class TestDatetime(unittest.TestCase):
         )
 
         for value in ((), [], {}, None, 1, 2.3):
-            self.assertEqual(f(value, "%Y"), dt.EPOCH)
+            self.assertEqual(f(value, "%Y"), dt.NONE)
 
     def test_parse_iso(self, f=dt.parse_iso):
         null = dt.from_ts(0)
@@ -140,12 +140,16 @@ class TestDatetime(unittest.TestCase):
             datetime.datetime(2019, 5, 7, 21, 25, 2),
         )
         self.assertEqual(
-            f("1970.01.01"),
+            f("1970-01-01"),
             dt.EPOCH,
         )
+        self.assertEqual(
+            f("1970.01.01"),
+            dt.NONE,
+        )
 
         for value in ((), [], {}, None, 1, 2.3):
-            self.assertEqual(f(value), dt.EPOCH)
+            self.assertEqual(f(value), dt.NONE)
 
     def test_parse_compat(self, f=dt.parse_compat):
         self.assertEqual(
@@ -153,6 +157,11 @@ class TestDatetime(unittest.TestCase):
             datetime.datetime(2019, 5, 7, 12, 25, 2),
         )
 
+    def test_none(self):
+        self.assertFalse(dt.NONE)
+        self.assertIsInstance(dt.NONE, dt.datetime)
+        self.assertEqual(str(dt.NONE), "0101-01-01 00:00:00")
+
 
 if __name__ == "__main__":
     unittest.main()

test/test_formatter.py

@@ -271,8 +271,8 @@ class TestFormatter(unittest.TestCase):
 
     def test_specifier_datetime(self):
         self._run_test("{ds:D%Y-%m-%dT%H:%M:%S%z}", "2010-01-01 00:00:00")
-        self._run_test("{ds:D%Y}", "1970-01-01 00:00:00")
-        self._run_test("{l:D%Y}", "1970-01-01 00:00:00")
+        self._run_test("{ds:D%Y}", "0101-01-01 00:00:00")
+        self._run_test("{l2:D%Y}", "0101-01-01 00:00:00")
 
     def test_specifier_offset(self):
         self._run_test("{dt:O 01:00}", "2010-01-01 01:00:00")