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class Computation: # pragma: no cover
"""
Computations produce a new column by performing a calculation on each row.
Computations are applied with :class:`.TableSet.compute`.
When implementing a custom computation, ensure that the values returned by
:meth:`.Computation.run` are of the type specified by
:meth:`.Computation.get_computed_data_type`. This can be ensured by using
the :meth:`.DataType.cast` method. See :class:`.Formula` for an example.
"""
def __str__(self):
"""
String representation of this column. May be used as a column name in
generated tables.
"""
return self.__class__.__name__
def get_computed_data_type(self, table):
"""
Returns an instantiated :class:`.DataType` which will be appended to
the table.
"""
raise NotImplementedError()
def validate(self, table):
"""
Perform any checks necessary to verify this computation can run on the
provided table without errors. This is called by :meth:`.Table.compute`
before :meth:`run`.
"""
pass
def run(self, table):
"""
When invoked with a table, returns a sequence of new column values.
"""
raise NotImplementedError()
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