Fix FlatMapTuple typehint bug

sdks/python/apache_beam/transforms/core.py

@@ -2238,7 +2238,7 @@ def FlatMapTuple(fn, *args, **kwargs):  # pylint: disable=invalid-name
   if defaults or args or kwargs:
     wrapper = lambda x, *args, **kwargs: fn(*(tuple(x) + args), **kwargs)
   else:
-    wrapper = lambda x: fn(*x)
+    wrapper = lambda x: fn(*tuple(x))
 
   # Proxy the type-hint information from the original function to this new
   # wrapped function.

sdks/python/apache_beam/typehints/typed_pipeline_test.py

@@ -21,6 +21,7 @@
 
 import typing
 import unittest
+from typing import Tuple
 
 import apache_beam as beam
 from apache_beam import pvalue
@@ -999,5 +1000,22 @@ def filter_fn(element: int) -> bool:
     self.assertEqual(th.output_types, ((int, ), {}))
 
 
+class TestFlatMapTuple(unittest.TestCase):
+  def test_flatmaptuple(self):
+    # Regression test. See
+    # https://github.com/apache/beam/issues/33014
+
+    def identity(x: Tuple[str, int]) -> Tuple[str, int]:
+      return x
+
+    with beam.Pipeline() as p:
+      # Just checking that this doesn't raise an exception.
+      (
+          p
+          | "Generate input" >> beam.Create([('P1', [2])])
+          | "Flat" >> beam.FlatMapTuple(lambda k, vs: [(k, v) for v in vs])
+          | "Identity" >> beam.Map(identity))
+
+
 if __name__ == '__main__':
   unittest.main()