[GitHub] [arrow] pitrou commented on a change in pull request #8317: ARROW-10134: [Python][Dataset] Add ParquetFileFragment.num_row_groups

[GitBox <gi...@apache.org>]

pitrou commented on a change in pull request #8317:
URL: https://github.com/apache/arrow/pull/8317#discussion_r499611181



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File path: python/pyarrow/_dataset.pyx
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@@ -962,6 +962,10 @@ cdef class ParquetFileFragment(FileFragment):
             return None
         return [RowGroupInfo.wrap(row_group) for row_group in c_row_groups]
 
+    @property
+    def num_row_groups(self):
+        return None if self.row_groups is None else len(self.row_groups)

Review comment:
       Is there a way to do this without reifying `self.row_groups`? Or is it cheap enough?




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