45 lines
1.3 KiB
Python
45 lines
1.3 KiB
Python
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#!/usr/bin/env python
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import six
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@six.python_2_unicode_compatible
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class Computation(object): # pragma: no cover
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"""
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Computations produce a new column by performing a calculation on each row.
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Computations are applied with :class:`.TableSet.compute`.
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When implementing a custom computation, ensure that the values returned by
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:meth:`.Computation.run` are of the type specified by
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:meth:`.Computation.get_computed_data_type`. This can be ensured by using
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the :meth:`.DataType.cast` method. See :class:`.Formula` 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_computed_data_type(self, table):
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"""
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Returns an instantiated :class:`.DataType` which will be appended to
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the table.
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"""
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raise NotImplementedError()
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def validate(self, table):
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"""
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Perform any checks necessary to verify this computation can run on the
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provided table without errors. This is called by :meth:`.Table.compute`
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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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When invoked with a table, returns a sequence of new column values.
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"""
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raise NotImplementedError()
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