saavannanavati commented on a change in pull request #12352:
URL: https://github.com/apache/beam/pull/12352#discussion_r466145176
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File path: sdks/python/apache_beam/runners/common.py
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@@ -1340,6 +1342,17 @@ def process_outputs(
self.per_element_output_counter.add_input(0)
return
+ if isinstance(results, (dict, str, unicode, bytes)):
+ results_type = type(results).__name__
+ raise TypeCheckError(
+ 'Returning a %s from a ParDo or FlatMap is '
+ 'discouraged. Please use list("%s") if you really '
+ 'want this behavior.' % (results_type, results))
+ elif not isinstance(results, collections.Iterable):
Review comment:
Out of curiosity, why is this check slow? Also, if we remove it, how
should we give the user the relevant error message?
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