[YAML] Add Partition transform.

sdks/python/apache_beam/yaml/programming_guide_test.py

@@ -404,6 +404,25 @@ def extract_timestamp(x):
           # [END setting_timestamp]
           ''')
 
+  def test_partition(self):
+    with beam.Pipeline(options=beam.options.pipeline_options.PipelineOptions(
+        pickle_library='cloudpickle')) as p:
+      elements = p | beam.Create([
+          beam.Row(percentile=1),
+          beam.Row(percentile=20),
+          beam.Row(percentile=90),
+      ])
+      _ = elements | YamlTransform(
+          '''
+          # [START model_multiple_pcollections_partition]
+          type: Partition
+          config:
+            by: str(percentile // 10)
+            language: python
+            outputs: ["0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "10"]
+          # [END model_multiple_pcollections_partition]
+          ''')
+
 
 if __name__ == '__main__':
   logging.getLogger().setLevel(logging.INFO)

sdks/python/apache_beam/yaml/readme_test.py

@@ -128,12 +128,25 @@ def expand(self, pcoll):
         lambda _: 1, sum, 'count')
 
 
+class _Fakes:
+  fn = str
+
+  class SomeTransform(beam.PTransform):
+    def __init__(*args, **kwargs):
+      pass
+
+    def expand(self, pcoll):
+      return pcoll
+
+
 RENDER_DIR = None
 TEST_TRANSFORMS = {
     'Sql': FakeSql,
     'ReadFromPubSub': FakeReadFromPubSub,
     'WriteToPubSub': FakeWriteToPubSub,
     'SomeGroupingTransform': FakeAggregation,
+    'SomeTransform': _Fakes.SomeTransform,
+    'AnotherTransform': _Fakes.SomeTransform,
 }
 
 
@@ -155,7 +168,7 @@ def input_file(self, name, content):
     return path
 
   def input_csv(self):
-    return self.input_file('input.csv', 'col1,col2,col3\nabc,1,2.5\n')
+    return self.input_file('input.csv', 'col1,col2,col3\na,1,2.5\n')
 
   def input_tsv(self):
     return self.input_file('input.tsv', 'col1\tcol2\tcol3\nabc\t1\t2.5\n')
@@ -250,13 +263,15 @@ def parse_test_methods(markdown_lines):
       else:
         if code_lines:
           if code_lines[0].startswith('- type:'):
+            is_chain = not any('input:' in line for line in code_lines)
             # Treat this as a fragment of a larger pipeline.
             # pylint: disable=not-an-iterable
             code_lines = [
                 'pipeline:',
-                '  type: chain',
+                '  type: chain' if is_chain else '',
                 '  transforms:',
                 '    - type: ReadFromCsv',
+                '      name: input',
                 '      config:',
                 '        path: whatever',
             ] + ['    ' + line for line in code_lines]
@@ -278,17 +293,6 @@ def createTestSuite(name, path):
     return type(name, (unittest.TestCase, ), dict(parse_test_methods(readme)))
 
 
-class _Fakes:
-  fn = str
-
-  class SomeTransform(beam.PTransform):
-    def __init__(*args, **kwargs):
-      pass
-
-    def expand(self, pcoll):
-      return pcoll
-
-
 # These are copied from $ROOT/website/www/site/content/en/documentation/sdks
 # at build time.
 YAML_DOCS_DIR = os.path.join(os.path.join(os.path.dirname(__file__), 'docs'))

sdks/python/apache_beam/yaml/yaml_mapping.py

@@ -24,6 +24,7 @@
 from typing import Callable
 from typing import Collection
 from typing import Dict
+from typing import List
 from typing import Mapping
 from typing import NamedTuple
 from typing import Optional
@@ -42,6 +43,7 @@
 from apache_beam.typehints import row_type
 from apache_beam.typehints import schemas
 from apache_beam.typehints import trivial_inference
+from apache_beam.typehints import typehints
 from apache_beam.typehints.row_type import RowTypeConstraint
 from apache_beam.typehints.schemas import named_fields_from_element_type
 from apache_beam.utils import python_callable
@@ -569,6 +571,86 @@ def extract_expr(name, v):
   return pcoll | sql_transform_constructor(query)
 
 
+@beam.ptransform.ptransform_fn
+def _Partition(
+    pcoll,
+    by: Union[str, Dict[str, str]],
+    outputs: List[str],
+    unknown_output: Optional[str] = None,
+    error_handling: Optional[Mapping[str, Any]] = None,
+    language: Optional[str] = 'generic'):
+  """Splits an input into several distinct outputs.
+
+  Each input element will go to a distinct output based on the field or
+  function given in the `by` configuration parameter.
+
+  Args:
+      by: A field, callable, or expression giving the destination output for
+        this element.  Should return a string that is a member of the `outputs`
+        parameter. If `unknown_output` is also set, other returns values are
+        accepted as well, otherwise an error will be raised.
+      outputs: The set of outputs into which this input is being partitioned.
+      unknown_output: (Optional) If set, indicates a destination output for any
+        elements that are not assigned an output listed in the `outputs`
+        parameter.
+      error_handling: (Optional) Whether and how to handle errors during
+        partitioning.
+      language: (Optional) The language of the `by` expression.
+  """
+  split_fn = _as_callable_for_pcoll(pcoll, by, 'by', language)
+  try:
+    split_fn_output_type = trivial_inference.infer_return_type(
+        split_fn, [pcoll.element_type])
+  except (TypeError, ValueError):
+    pass
+  else:
+    if not typehints.is_consistent_with(split_fn_output_type,
+                                        typehints.Optional[str]):
+      raise ValueError(
+          f'Partition function "{by}" must return a string type '
+          f'not {split_fn_output_type}')
+  error_output = error_handling['output'] if error_handling else None
+  if error_output in outputs:
+    raise ValueError(
+        f'Error handling output "{error_output}" '
+        f'cannot be among the listed outputs {outputs}')
+  T = TypeVar('T')
+
+  def split(element):
+    tag = split_fn(element)
+    if tag is None:
+      tag = unknown_output
+    if not isinstance(tag, str):
+      raise ValueError(
+          f'Returned output name "{tag}" of type {type(tag)} '
+          f'from "{by}" must be a string.')
+    if tag not in outputs:
+      if unknown_output:
+        tag = unknown_output
+      else:
+        raise ValueError(f'Unknown output name "{tag}" from {by}')
+    return beam.pvalue.TaggedOutput(tag, element)
+
+  output_set = set(outputs)
+  if unknown_output:
+    output_set.add(unknown_output)
+  if error_output:
+    output_set.add(error_output)
+  mapping_transform = beam.Map(split)
+  if error_output:
+    mapping_transform = mapping_transform.with_exception_handling(
+        **exception_handling_args(error_handling))
+  else:
+    mapping_transform = mapping_transform.with_outputs(*output_set)
+  splits = pcoll | mapping_transform.with_input_types(T).with_output_types(T)
+  result = {out: getattr(splits, out) for out in output_set}
+  if error_output:
+    result[
+        error_output] = result[error_output] | _map_errors_to_standard_format(
+            pcoll.element_type)
+  return result
+
+
 @beam.ptransform.ptransform_fn
 @maybe_with_exception_handling_transform_fn
 def _AssignTimestamps(
@@ -588,7 +670,8 @@ def _AssignTimestamps(
   Args:
       timestamp: A field, callable, or expression giving the new timestamp.
       language: The language of the timestamp expression.
-      error_handling: Whether and how to handle errors during iteration.
+      error_handling: Whether and how to handle errors during timestamp
+        evaluation.
   """
   timestamp_fn = _as_callable_for_pcoll(pcoll, timestamp, 'timestamp', language)
   T = TypeVar('T')
@@ -611,6 +694,9 @@ def create_mapping_providers():
           'MapToFields-python': _PyJsMapToFields,
           'MapToFields-javascript': _PyJsMapToFields,
           'MapToFields-generic': _PyJsMapToFields,
+          'Partition-python': _Partition,
+          'Partition-javascript': _Partition,
+          'Partition-generic': _Partition,
       }),
       yaml_provider.SqlBackedProvider({
           'Filter-sql': _SqlFilterTransform,