Omit 0 as fractional epoch seconds

This updates unix timestamp serialization to omit fractional seconds
when that fraction is 0.

Author: JordonPhillips

codegen/smithy-python-codegen/src/main/java/software/amazon/smithy/python/codegen/integration/HttpProtocolGeneratorUtils.java

@@ -60,7 +60,9 @@ public static String getTimestampInputParam(
                 writer.addImport("smithy_python.utils", "serialize_rfc3339");
                 return String.format("serialize_rfc3339(%s)", result);
             case EPOCH_SECONDS:
-                return "str(" + result + ".timestamp())";
+                writer.addDependency(SmithyPythonDependency.SMITHY_PYTHON);
+                writer.addImport("smithy_python.utils", "serialize_epoch_seconds");
+                return String.format("serialize_epoch_seconds(%s)", result);
             case HTTP_DATE:
                 writer.addStdlibImport("email.utils", "format_datetime");
                 return "format_datetime(" + result + ", usegmt=True)";

python-packages/smithy-python/smithy_python/utils.py

@@ -166,3 +166,17 @@ def serialize_rfc3339(given: datetime) -> str:
         return given.strftime(RFC3339_MICRO)
     else:
         return given.strftime(RFC3339)
+
+
+def serialize_epoch_seconds(given: datetime) -> str:
+    """Serializes a datetime into a string containing the epoch seconds.
+
+    If ``microseconds`` is 0, no fractional part is serialized.
+
+    :param given: The datetime to serialize.
+    :retursn: A string containing the seconds since the UNIX epoch.
+    """
+    result = given.timestamp()
+    if given.microsecond == 0:
+        result = int(result)
+    return str(result)

python-packages/smithy-python/tests/unit/test_utils.py

@@ -10,6 +10,7 @@
     ensure_utc,
     expect_type,
     limited_parse_float,
+    serialize_epoch_seconds,
     serialize_float,
     serialize_rfc3339,
     split_every,
@@ -189,3 +190,17 @@ def test_serialize_float(given: float | Decimal, expected: str) -> None:
 )
 def test_serialize_rfc3339(given: datetime, expected: str) -> None:
     assert serialize_rfc3339(given) == expected
+
+
+@pytest.mark.parametrize(
+    "given, expected",
+    [
+        (datetime(2017, 1, 1, tzinfo=timezone.utc), "1483228800"),
+        (
+            datetime(2017, 1, 1, microsecond=1, tzinfo=timezone.utc),
+            "1483228800.000001",
+        ),
+    ],
+)
+def test_serialize_epoch_seconds(given: datetime, expected: str) -> None:
+    assert serialize_epoch_seconds(given) == expected