fix: make check_date_operators work with dateutil < 2.8.1 (#273)

UnleashClient/constraints/Constraint.py

@@ -1,10 +1,10 @@
 # pylint: disable=invalid-name, too-few-public-methods, use-a-generator
 from datetime import datetime
 from enum import Enum
-from typing import Optional, Union
+from typing import Any, Optional, Union
 
 import semver
-from dateutil.parser import ParserError, parse
+from dateutil.parser import parse
 
 from UnleashClient.utils import LOGGER, get_identifier
 
@@ -123,13 +123,22 @@ def check_date_operators(self, context_value: Union[datetime, str]) -> bool:
         return_value = False
         parsing_exception = False
 
+        DateUtilParserError: Any
+
+        try:
+            from dateutil.parser import ParserError
+
+            DateUtilParserError = ParserError
+        except ImportError:
+            DateUtilParserError = ValueError
+
         try:
             parsed_date = parse(self.value)
             if isinstance(context_value, str):
                 context_date = parse(context_value)
             else:
                 context_date = context_value
-        except ParserError:
+        except DateUtilParserError:
             LOGGER.error(f"Unable to parse date: {self.value}")
             parsing_exception = True