ColumnLiteral

class lsst.daf.relation.ColumnLiteral(value: Any, dtype: type | None[type, None])

Bases: lsst.daf.relation.ColumnExpression

A concrete column expression backed by a regular Python value.

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.