altair.param(name=None, value=Undefined, bind=Undefined, empty=Undefined, expr=Undefined, **kwds)#

Create a named parameter. See for examples. Although both variable parameters and selection parameters can be created using this ‘param’ function, to create a selection parameter, it is recommended to use either ‘selection_point’ or ‘selection_interval’ instead.

namestring (optional)

The name of the parameter. If not specified, a unique name will be created.

valueany (optional)

The default value of the parameter. If not specified, the parameter will be created without a default value.

bindBinding (optional)

Binds the parameter to an external input element such as a slider, selection list or radio button group.

emptyboolean (optional)

For selection parameters, the predicate of empty selections returns True by default. Override this behavior, by setting this property ‘empty=False’.

exprstr, Expression (optional)

An expression for the value of the parameter. This expression may include other parameters, in which case the parameter will automatically update in response to upstream parameter changes.


additional keywords will be used to construct a parameter. If ‘select’ is among the keywords, then a selection parameter will be created. Otherwise, a variable parameter will be created.

parameter: Parameter

The parameter object that can be used in chart creation.