52 lines
1.7 KiB
Python
52 lines
1.7 KiB
Python
#!/usr/bin/env python
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import six
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from agate.exceptions import UnsupportedAggregationError
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@six.python_2_unicode_compatible
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class Aggregation(object): # pragma: no cover
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"""
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Aggregations create a new value by summarizing a :class:`.Column`.
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Aggregations are applied with :meth:`.Table.aggregate` and
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:meth:`.TableSet.aggregate`.
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When creating a custom aggregation, ensure that the values returned by
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:meth:`.Aggregation.run` are of the type specified by
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:meth:`.Aggregation.get_aggregate_data_type`. This can be ensured by using
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the :meth:`.DataType.cast` method. See :class:`.Summary` for an example.
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"""
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def __str__(self):
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"""
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String representation of this column. May be used as a column name in
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generated tables.
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"""
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return self.__class__.__name__
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def get_aggregate_data_type(self, table):
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"""
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Get the data type that should be used when using this aggregation with
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a :class:`.TableSet` to produce a new column.
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Should raise :class:`.UnsupportedAggregationError` if this column does
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not support aggregation into a :class:`.TableSet`. (For example, if it
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does not return a single value.)
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"""
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raise UnsupportedAggregationError()
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def validate(self, table):
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"""
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Perform any checks necessary to verify this aggregation can run on the
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provided table without errors. This is called by
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:meth:`.Table.aggregate` before :meth:`run`.
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"""
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pass
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def run(self, table):
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"""
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Execute this aggregation on a given column and return the result.
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"""
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raise NotImplementedError()
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