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Access experimental variables

class var

The var object provides access to experimental variables. Experimental variables are the variables that live in the GUI, and are commonly set as independent variables in the loop item, referred to using the square-bracket ([my_variable]) notation, and logged by the logger item.

In addition to the functions listed below, the following semantics are supported:

Example:

# Set an experimental variable
var.my_variable = u'my_value'
# Get an experimental variable
print(u'Subject nr = %d' % var.subject_nr)
# Delete (unset) an experimental variable
del var.my_variable
# Check if an experimental variable exists
if u'my_variable' in var:
    print(u'my_variable exists!')
# Loop through all experimental variables
for var_name in var:
        print(u'variable found: %s' % var_name)

function var.clear(preserve=[])

New in 3.1.2

Clears all experimentals variables.

Keywords:

  • preserve -- A list of variable names

function var.get(var, default=None, _eval=True, valid=None)

Gets an experimental variable.

Example:

print('my_variable = %s' % var.get(u'my_variable'))
# Equivalent to:
print('my_variable = %s' % var.my_variable)
# But if you want to pass keyword arguments you need to use `get()`:
var.get(u'my_variable', default=u'a_default_value')

Arguments:

  • var -- The variable to retrieve.
    • Type: str, unicode

Keywords:

  • default -- A default value in case the variable doesn't exist, or None for no default value.
    • Type: any
    • Default: None
  • _eval -- Determines whether the returned should be evaluated for variable references.
    • Type: bool
    • Default: True
  • valid -- A list of valid values, or None to allow all values.
    • Type: NoneType, list
    • Default: None

function var.has(var)

Checks if an experimental variable exists.

Example:

if var.has(u'my_variable'):
        print(u'my_variable has been defined!')
# Equivalent to:
if u'my_variable' in var:
        print(u'my_variable has been defined!')

Arguments:

  • var -- The variable to check.
    • Type: str, unicode

function var.items()

Returns a list of (variable_name, value) tuples. See vars for a note about the non-exhaustiveness of this function.

Returns:

A list of (variable_name, value) tuples.

  • Type: list

function var.set(var, val)

Sets and experimental variable.

Example:

var.set(u'my_variable', u'my_value')
# Equivalent to
var.my_variable = u'my_value'

Arguments:

  • var -- The variable to assign.
    • Type: str, unicode
  • val -- The value to assign.
    • Type: any

function var.unset(var)

Deletes a variable.

Example:

var.unset(u'my_variable')
# Equivalent to:
del var.my_variable

Arguments:

  • var -- The variable to delete.
    • Type: str, unicode

function var.vars()

Returns a list of experimental variables. Because experimental variables can be stored in multiple places, this list may not be exhaustive. That is, u'my_var' in var may return True, while u'my_var' is not in the list of variables as returned by this function.

Returns:

A list of variable names.

  • Type: list