Fix compatibility with Python 3.8+

Author: sdispater

pendulum/datetime.py

@@ -39,6 +39,7 @@
 from .tz import UTC
 from .tz.timezone import FixedTimezone
 from .tz.timezone import Timezone
+from .utils._compat import PY38
 
 
 class DateTime(datetime.datetime, Date):
@@ -1147,6 +1148,16 @@ def __add__(self, other: datetime.timedelta) -> "DateTime":
         if not isinstance(other, datetime.timedelta):
             return NotImplemented
 
+        if PY38:
+            # This is a workaround for Python 3.8+
+            # since calling astimezone() will call this method
+            # instead of the base datetime class one.
+            import inspect
+
+            caller = inspect.stack()[1][3]
+            if caller == "astimezone":
+                return super().__add__(other)
+
         return self._add_timedelta_(other)
 
     def __radd__(self, other: datetime.timedelta) -> "DateTime":

pendulum/utils/_compat.py

@@ -2,6 +2,7 @@
 
 
 PYPY = hasattr(sys, "pypy_version_info")
+PY38 = sys.version_info[:2] >= (3, 8)
 
 
 try:

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 isolated_build = true
-envlist = py36, py37, py38, pypy3
+envlist = py36, py37, py38, py39, pypy3
 
 [testenv]
 whitelist_externals = poetry