ColumnFunction¶

class lsst.daf.relation.ColumnFunction(name: str, args: tuple[ColumnExpression, ...], dtype: type | None, supporting_engine_types: tuple[type[Engine], ...] | None)¶

Bases: lsst.daf.relation.ColumnExpression

A concrete column expression that represents calling a named function with column expression arguments.

Attributes Summary

columns_required Columns required by this expression (Set [ ColumnTag ]).

Methods Summary

`eq`(other)	Construct a boolean equality-comparison expression.
`function`(name, *args, dtype, …)	Construct an expression that represents a function call with expression arguments.
`ge`(other)	Construct a boolean greater-or-equal-comparison expression.
`gt`(other)	Construct a boolean greater-than-comparison expression.
`is_supported_by`(engine)	Test whether the given engine is capable of evaluating this expression.
`le`(other)	Construct a boolean less-or-equal-comparison expression.
`literal`(value, dtype, None] = None)	Construct an expression backed by a regular Python object.
`lt`(other)	Construct a boolean less-than-comparison expression.
`method`(name, *args, dtype, …)	Construct an expression that represents a method call with expression arguments.
`ne`(other)	Construct a boolean inequality-comparison expression.
`predicate_function`(name, *args, …)	Construct an expression that represents a function call with expression arguments and a boolean result.
`predicate_method`(name, *args, …)	Construct an expression that represents a method call with expression arguments and a boolean result.
`reference`(tag, dtype, None] = None)	Construct an expression that refers to a column in a relation.

Attributes Documentation

columns_required¶

Columns required by this expression (Set [ ColumnTag ]).

This includes columns required by expressions nested within this one.

Methods Documentation

eq(other: lsst.daf.relation._columns._expression.ColumnExpression) → lsst.daf.relation._columns._expression.PredicateFunction¶

Construct a boolean equality-comparison expression.

Parameters:	other : `ColumnExpression` Expression whose value will be compared to that of `self`.
Returns:	comparison : `Predicate` Boolean column expression.

classmethod function(name: str, *args, dtype: type | None = None, supporting_engine_types: Iterable[type[Engine]] | None = None) → ColumnFunction¶

Construct an expression that represents a function call with expression arguments.

Parameters:

name : str: Name of the method, to be interpreted by the Engine or other algorithm.
*args : ColumnExpression: Expressions to pass as arguments to the method (not including self; this is a classmethod, so it never has access to self).
dtype : type or None, optional: The Python type this expression evaluates to (type or None).
supporting_engine_types : Iterable [ type ], optional: If provided, the set of Engine types that are expected to support this expression. If None (default), all engines are assumed to support it.

Returns:

function : ColumnFunction: Column expression that represents this function call.

ge(other: lsst.daf.relation._columns._expression.ColumnExpression) → lsst.daf.relation._columns._expression.PredicateFunction¶

Construct a boolean greater-or-equal-comparison expression.

Parameters:	other : `ColumnExpression` Expression whose value will be compared to that of `self`.
Returns:	comparison : `Predicate` Boolean column expression.

gt(other: lsst.daf.relation._columns._expression.ColumnExpression) → lsst.daf.relation._columns._expression.PredicateFunction¶

Construct a boolean greater-than-comparison expression.

Parameters:	other : `ColumnExpression` Expression whose value will be compared to that of `self`.
Returns:	comparison : `Predicate` Boolean column expression.

is_supported_by(engine: Engine) → bool¶

Test whether the given engine is capable of evaluating this expression.

Parameters:	engine : `Engine` Engine to test.
Returns:	supported : `bool` Whether the engine supports this expression and all expressions nested within it.

le(other: lsst.daf.relation._columns._expression.ColumnExpression) → lsst.daf.relation._columns._expression.PredicateFunction¶

Construct a boolean less-or-equal-comparison expression.

Parameters:	other : `ColumnExpression` Expression whose value will be compared to that of `self`.
Returns:	comparison : `Predicate` Boolean column expression.

classmethod literal(value: Any, dtype: Optional[type, None] = None) → lsst.daf.relation._columns._expression.ColumnLiteral¶

Construct an expression backed by a regular Python object.

Parameters:	value Value for the expression. dtype : `type` or `None`, optional The Python type this expression evaluates to (`type` or `None`).
Returns:	literal : `ColumnLiteral` A column expression backed by the given value.

lt(other: lsst.daf.relation._columns._expression.ColumnExpression) → lsst.daf.relation._columns._expression.PredicateFunction¶

Construct a boolean less-than-comparison expression.

Parameters:	other : `ColumnExpression` Expression whose value will be compared to that of `self`.
Returns:	comparison : `Predicate` Boolean column expression.

method(name: str, *args, dtype: type | None = None, supporting_engine_types: Iterable[type[Engine]] | None = None) → ColumnFunction¶

Construct an expression that represents a method call with expression arguments.

Parameters:

name : str: Name of the method, to be interpreted by the Engine or other algorithm.
*args : ColumnExpression: Expressions to pass as arguments to the method (after self).
dtype : type or None, optional: The Python type this expression evaluates to (type or None).
supporting_engine_types : Iterable [ type ], optional: If provided, the set of Engine types that are expected to support this expression. If None (default), all engines are assumed to support it.

Returns:

function : ColumnFunction: Column expression that represents this function call.

Notes

ColumnExpression cannot actually force an engine to interpret the given name as the name of a method rather than something else; calling this method like this:

a.method("name", b)

is exactly equivalent to:

ColumnExpression.function("name", a, b)

The provided iteration and sql engines both interpret these names as method names if and only if they are not first found in the built-in operator module.

ne(other: lsst.daf.relation._columns._expression.ColumnExpression) → lsst.daf.relation._columns._expression.PredicateFunction¶

Construct a boolean inequality-comparison expression.

Parameters:	other : `ColumnExpression` Expression whose value will be compared to that of `self`.
Returns:	comparison : `Predicate` Boolean column expression.

classmethod predicate_function(name: str, *args, supporting_engine_types: Iterable[type[Engine]] | None = None) → PredicateFunction¶

Construct an expression that represents a function call with expression arguments and a boolean result.

Parameters:

name : str: Name of the method, to be interpreted by the Engine or other algorithm.
*args : ColumnExpression: Expressions to pass as arguments to the method (not including self; this is a classmethod, so it never has access to self).
dtype : type or None, optional: The Python type this expression evaluates to (type or None).
supporting_engine_types : Iterable [ type ], optional: If provided, the set of Engine types that are expected to support this expression. If None (default), all engines are assumed to support it.

Returns:

function : PredicateFunction: Boolean column expression that represents this function call.

predicate_method(name: str, *args, supporting_engine_types: Set[type[Engine]] | None = None) → PredicateFunction¶

Construct an expression that represents a method call with expression arguments and a boolean result.

Parameters:

name : str: Name of the method, to be interpreted by the Engine or other algorithm.
*args : ColumnExpression: Expressions to pass as arguments to the method (after self).
dtype : type or None, optional: The Python type this expression evaluates to (type or None).
supporting_engine_types : Iterable [ type ] optional: If provided, the set of Engine types that are expected to support this expression. If None (default), all engines are assumed to support it.

Returns:

function : PredicateFunction: Boolean column expression that represents this function call.

Notes

ColumnExpression cannot actually force an engine to interpret the given name as the name of a method rather than something else; calling this method like this:

a.predicate_method("name", b)

is exactly equivalent to:

ColumnExpression.predicate_function("name", a, b)

The provided iteration and sql engines both interpret these names as method names if and only if they are not first found in the built-in operator module.

classmethod reference(tag: lsst.daf.relation._columns._tag.ColumnTag, dtype: Optional[type, None] = None) → lsst.daf.relation._columns._expression.ColumnReference¶

Construct an expression that refers to a column in a relation.

Parameters:	tag : `ColumnTag` Identifier for the column to reference. dtype : `type` or `None`, optional The Python type this expression evaluates to (`type` or `None`).
Returns:	reference : `ColumnReference` A column expression that refers the given relation column.

Navigation

ColumnFunction¶