[jira] [Resolved] (ARROW-4076) [Python] schema validation and filters

["Wes McKinney (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ARROW-4076?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Wes McKinney resolved ARROW-4076.
---------------------------------
    Resolution: Fixed

Issue resolved by pull request 4600
[https://github.com/apache/arrow/pull/4600]

> [Python] schema validation and filters
> --------------------------------------
>
>                 Key: ARROW-4076
>                 URL: https://issues.apache.org/jira/browse/ARROW-4076
>             Project: Apache Arrow
>          Issue Type: Bug
>          Components: Python
>            Reporter: George Sakkis
>            Assignee: Joris Van den Bossche
>            Priority: Minor
>              Labels: datasets, easyfix, parquet, pull-request-available
>             Fix For: 0.14.0
>
>          Time Spent: 1h
>  Remaining Estimate: 0h
>
> Currently [schema validation|https://github.com/apache/arrow/blob/758bd557584107cb336cbc3422744dacd93978af/python/pyarrow/parquet.py#L900] of {{ParquetDataset}} takes place before filtering. This may raise a {{ValueError}} if the schema is different in some dataset pieces, even if these pieces would be subsequently filtered out. I think validation should happen after filtering to prevent such spurious errors:
> {noformat}
> --- a/pyarrow/parquet.py	
> +++ b/pyarrow/parquet.py	
> @@ -878,13 +878,13 @@
>          if split_row_groups:
>              raise NotImplementedError("split_row_groups not yet implemented")
>  
> -        if validate_schema:
> -            self.validate_schemas()
> -
>          if filters is not None:
>              filters = _check_filters(filters)
>              self._filter(filters)
>  
> +        if validate_schema:
> +            self.validate_schemas()
> +
>      def validate_schemas(self):
>          open_file = self._get_open_file_func()
> {noformat}



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