chore: drop use of 'pytz' in tests / examples (googleapis#534)

Current (pre-)releases of 'google-api-core' and 'google-cloud-core' no
longer use or depend on 'pytz'.

Closes googleapis#533.

google/cloud/storage/client.py

@@ -1613,10 +1613,10 @@ def generate_signed_post_policy_v4(
         Example:
             Generate signed POST policy and upload a file.
 
+            >>> import datetime
             >>> from google.cloud import storage
-            >>> import pytz
             >>> client = storage.Client()
-            >>> tz = pytz.timezone('America/New_York')
+            >>> tz = datetime.timezone(datetime.timedelta(hours=1), 'CET')
             >>> policy = client.generate_signed_post_policy_v4(
                 "bucket-name",
                 "blob-name",

tests/unit/test__signing.py

@@ -44,6 +44,24 @@ def _utc_seconds(when):
     return int(calendar.timegm(when.timetuple()))
 
 
+def _make_cet_timezone():
+    try:
+        from datetime import timezone
+
+    except ImportError:  # Python 2.7
+        from google.cloud._helpers import _UTC
+
+        class CET(_UTC):
+            _tzname = "CET"
+            _utcoffset = datetime.timedelta(hours=1)
+
+        return CET()
+    else:
+        from datetime import timedelta
+
+        return timezone(timedelta(hours=1), name="CET")
+
+
 class Test_get_expiration_seconds_v2(unittest.TestCase):
     @staticmethod
     def _call_fut(expiration):
@@ -81,13 +99,7 @@ def test_w_expiration_utc_datetime(self):
         self.assertEqual(self._call_fut(expiration_utc), utc_seconds)
 
     def test_w_expiration_other_zone_datetime(self):
-        from google.cloud._helpers import _UTC
-
-        class CET(_UTC):
-            _tzname = "CET"
-            _utcoffset = datetime.timedelta(hours=1)
-
-        zone = CET()
+        zone = _make_cet_timezone()
         expiration_other = datetime.datetime(2004, 8, 19, 0, 0, 0, 0, zone)
         utc_seconds = _utc_seconds(expiration_other)
         cet_seconds = utc_seconds - (60 * 60)  # CET one hour earlier than UTC
@@ -198,13 +210,8 @@ def test_w_expiration_utc_datetime(self):
 
     def test_w_expiration_other_zone_datetime(self):
         from google.cloud._helpers import UTC
-        from google.cloud._helpers import _UTC
-
-        class CET(_UTC):
-            _tzname = "CET"
-            _utcoffset = datetime.timedelta(hours=1)
 
-        zone = CET()
+        zone = _make_cet_timezone()
         fake_utcnow = datetime.datetime(2004, 8, 19, 0, 0, 0, 0, UTC)
         fake_cetnow = fake_utcnow.astimezone(zone)
         delta = datetime.timedelta(seconds=10)

tests/unit/test_bucket.py

@@ -366,10 +366,10 @@ def test_ctor_defaults(self):
 
     def test_ctor_explicit_ubla(self):
         import datetime
-        import pytz
+        from google.cloud._helpers import UTC
 
         bucket = self._make_bucket()
-        now = datetime.datetime.utcnow().replace(tzinfo=pytz.UTC)
+        now = datetime.datetime.utcnow().replace(tzinfo=UTC)
 
         config = self._make_one(
             bucket,
@@ -403,10 +403,10 @@ def test_ctor_explicit_pap(self):
 
     def test_ctor_explicit_bpo(self):
         import datetime
-        import pytz
+        from google.cloud._helpers import UTC
 
         bucket = self._make_bucket()
-        now = datetime.datetime.utcnow().replace(tzinfo=pytz.UTC)
+        now = datetime.datetime.utcnow().replace(tzinfo=UTC)
 
         config = pytest.deprecated_call(
             self._make_one,
@@ -433,10 +433,10 @@ def test_ctor_ubla_and_bpo_enabled(self):
 
     def test_ctor_ubla_and_bpo_time(self):
         import datetime
-        import pytz
+        from google.cloud._helpers import UTC
 
         bucket = self._make_bucket()
-        now = datetime.datetime.utcnow().replace(tzinfo=pytz.UTC)
+        now = datetime.datetime.utcnow().replace(tzinfo=UTC)
 
         with self.assertRaises(ValueError):
             self._make_one(
@@ -481,12 +481,12 @@ def test_from_api_repr_w_disabled(self):
 
     def test_from_api_repr_w_enabled(self):
         import datetime
-        import pytz
+        from google.cloud._helpers import UTC
         from google.cloud._helpers import _datetime_to_rfc3339
 
         klass = self._get_target_class()
         bucket = self._make_bucket()
-        now = datetime.datetime.utcnow().replace(tzinfo=pytz.UTC)
+        now = datetime.datetime.utcnow().replace(tzinfo=UTC)
         resource = {
             "uniformBucketLevelAccess": {
                 "enabled": True,
@@ -2174,11 +2174,11 @@ def test_iam_configuration_policy_missing(self):
 
     def test_iam_configuration_policy_w_entry(self):
         import datetime
-        import pytz
+        from google.cloud._helpers import UTC
         from google.cloud._helpers import _datetime_to_rfc3339
         from google.cloud.storage.bucket import IAMConfiguration
 
-        now = datetime.datetime.utcnow().replace(tzinfo=pytz.UTC)
+        now = datetime.datetime.utcnow().replace(tzinfo=UTC)
         NAME = "name"
         properties = {
             "iamConfiguration": {

tests/unit/test_client.py

@@ -1778,7 +1778,7 @@ def _create_hmac_key_helper(
         self, explicit_project=None, user_project=None, timeout=None, retry=None,
     ):
         import datetime
-        from pytz import UTC
+        from google.cloud._helpers import UTC
         from google.cloud.storage.hmac_key import HMACKeyMetadata
 
         project = "PROJECT"

tests/unit/test_hmac_key.py

@@ -173,7 +173,7 @@ def test_state_setter_active(self):
 
     def test_time_created_getter(self):
         import datetime
-        from pytz import UTC
+        from google.cloud._helpers import UTC
 
         metadata = self._make_one()
         now = datetime.datetime.utcnow()
@@ -183,7 +183,7 @@ def test_time_created_getter(self):
 
     def test_updated_getter(self):
         import datetime
-        from pytz import UTC
+        from google.cloud._helpers import UTC
 
         metadata = self._make_one()
         now = datetime.datetime.utcnow()