ColumnFunction

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

Bases: 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])	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])	Construct an expression that refers to a column in a relation.

Attributes Documentation

columns_required

Methods Documentation

eq(other: ColumnExpression) → PredicateFunction

Construct a boolean equality-comparison expression.

Parameters:

otherColumnExpression

Expression whose value will be compared to that of self.

Returns:

comparisonPredicate

Boolean column expression.

classmethod function(name: str, *args: ColumnExpression, 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:

namestr

Name of the method, to be interpreted by the Engine or other algorithm.

*argsColumnExpression

Expressions to pass as arguments to the method (not including self; this is a classmethod, so it never has access to self).

dtypetype or None, optional

The Python type this expression evaluates to (type or None).

supporting_engine_typesIterable [ 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:

functionColumnFunction

Column expression that represents this function call.

ge(other: ColumnExpression) → PredicateFunction

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

Parameters:

otherColumnExpression

Expression whose value will be compared to that of self.

Returns:

comparisonPredicate

Boolean column expression.

gt(other: ColumnExpression) → PredicateFunction

Construct a boolean greater-than-comparison expression.

Parameters:

otherColumnExpression

Expression whose value will be compared to that of self.

Returns:

comparisonPredicate

Boolean column expression.

is_supported_by(engine: Engine) → bool

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

Parameters:

engineEngine

Engine to test.

Returns:

supportedbool

Whether the engine supports this expression and all expressions nested within it.

le(other: ColumnExpression) → PredicateFunction

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

Parameters:

otherColumnExpression

Expression whose value will be compared to that of self.

Returns:

comparisonPredicate

Boolean column expression.

classmethod literal(value: Any, dtype: type | None = None) → ColumnLiteral

Construct an expression backed by a regular Python object.

Parameters:

value

Value for the expression.

dtypetype or None, optional

The Python type this expression evaluates to (type or None).

Returns:

literalColumnLiteral

A column expression backed by the given value.

lt(other: ColumnExpression) → PredicateFunction

Construct a boolean less-than-comparison expression.

Parameters:

otherColumnExpression

Expression whose value will be compared to that of self.

Returns:

comparisonPredicate

Boolean column expression.

method(name: str, *args: ColumnExpression, 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:

namestr

Name of the method, to be interpreted by the Engine or other algorithm.

*argsColumnExpression

Expressions to pass as arguments to the method (after self).

dtypetype or None, optional

The Python type this expression evaluates to (type or None).

supporting_engine_typesIterable [ 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:

functionColumnFunction

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: ColumnExpression) → PredicateFunction

Construct a boolean inequality-comparison expression.

Parameters:

otherColumnExpression

Expression whose value will be compared to that of self.

Returns:

comparisonPredicate

Boolean column expression.

classmethod predicate_function(name: str, *args: ColumnExpression, 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:

namestr

Name of the method, to be interpreted by the Engine or other algorithm.

*argsColumnExpression

Expressions to pass as arguments to the method (not including self; this is a classmethod, so it never has access to self).

dtypetype or None, optional

The Python type this expression evaluates to (type or None).

supporting_engine_typesIterable [ 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:

functionPredicateFunction

Boolean column expression that represents this function call.

predicate_method(name: str, *args: ColumnExpression, 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:

namestr

Name of the method, to be interpreted by the Engine or other algorithm.

*argsColumnExpression

Expressions to pass as arguments to the method (after self).

dtypetype or None, optional

The Python type this expression evaluates to (type or None).

supporting_engine_typesIterable [ 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:

functionPredicateFunction

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: ColumnTag, dtype: type | None = None) → ColumnReference

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

Parameters:

tagColumnTag

Identifier for the column to reference.

dtypetype or None, optional

The Python type this expression evaluates to (type or None).

Returns:

referenceColumnReference

A column expression that refers the given relation column.