# Global options¶

The GlobalOptions class provides a generic mechanism for setting and accessing global options for parents in one or several related classes, typically for customizing the representation of their elements. This class will eventually also support setting options on a parent by parent basis.

These options should be “attached” to one or more classes as an options method.

For good examples of GlobalOptions in action see sage.combinat.partition.Partitions.options() and sage.combinat.tableau.Tableaux.options().

## Construction of options classes¶

The general setup for creating a set of global options is:

sage: from sage.structure.global_options import GlobalOptions
sage: class MyOptions(GlobalOptions):
....:     '''
....:     Nice options
....:
....:     @[email protected]
....:     '''
....:     NAME = 'option name'
....:     module = 'sage.some_module.some_file'
....:     option_class = 'name_of_class_controlled_by_options'
....:     first_option = dict(default='with_bells',
....:                       description='Changes the functionality of _repr_',
....:                       values=dict(with_bells='causes _repr_ to print with bells',
....:                                   with_whistles='causes _repr_ to print with whistles'),
....:                       alias=dict(bells='option1', whistles='option2'))
....:     # second_option = dict(...)
....:     # third_option = dict(...)


Note the syntax using the class keyword. However, because of some metaclass magic, the resulting MyOptions object becomes an instance of GlobalOptions instead of a subclass. So, despite the class syntax, MyOptions is not a class.

The options constructed by GlobalOptions have to be explicitly associated to the class that they control using the following arguments:

• NAME – A descriptive name for the options class. This is optional; the default is the name of the constructed class.
• module – The sage module containing the options class (optional)
• option_class – The name of the options class. This is optional and defaults to NAME if not explicitly set.

It is only possible to pickle a GlobalOptions class if the corresponding module is specified and if the options are explicitly attached to the corresponding class as a options method.

Each option is specified as a dictionary which describes the possible values for the option and its documentation. The possible entries in this dictionary are:

• alias – Allows for several option values to do the same thing.
• alt_name – An alternative name for this option.
• checker – A validation function which returns whether a user supplied value is valid or not. This is typically useful for large lists of legal values such as NN.
• default – Gives the default value for the option.
• description – A one line description of the option.
• link_to – Links this option to another one in another set of global options. This is used for example to allow Partitions and Tableaux to share the same convention option.
• setter – A function which is called after the value of the option is changed.
• values – A dictionary assigning each valid value for the option to a short description of what it does.
• case_sensitive – (Default: True) True or False depending on whether the values of the option are case sensitive.

For each option, either a complete list of possible values, via values, or a validation function, via checker, must be given. The values can be quite arbitrary, including user-defined functions which customize the default behaviour of the classes such as the output of _repr_ or latex(). See Dispatchers below, and _dispatcher(), for more information.

The documentation for the options is automatically constructed from the docstring of the class by replacing the magic word @OPTIONS@ with a description of each option.

The basic structure for defining a GlobalOptions class is best illustrated by an example:

sage: from sage.structure.global_options import GlobalOptions
....:     class options(GlobalOptions):
....:         '''
....:         Fancy documentation
....:         -------------------
....:
....:         @[email protected]
....:
....:         The END!
....:         '''
....:         entree = dict(default='soup',
....:                     description='The first course of a meal',
....:                     values=dict(soup='soup of the day', bread='oven baked'),
....:         appetizer = dict(alt_name='entree')
....:         main = dict(default='pizza', description='Main meal',
....:                   values=dict(pizza='thick crust', pasta='penne arrabiata'),
....:                   case_sensitive=False)
....:         dessert = dict(default='espresso', description='Dessert',
....:                      values=dict(espresso='life begins again',
....:                                  cake='waist begins again',
....:                                  cream='fluffy, white stuff'))
....:         tip = dict(default=10, description='Reward for good service',
....:                    checker = lambda tip: tip in range(0,20))
- dessert: espresso
- entree:  soup
- main:    pizza
- tip:     10


In the examples above, the options are constructed when the options object is created. However, it is also possible to construct the options dynamically using the GlobalOptions._add_to_options() methods.

For more details see GlobalOptions.

## Accessing and setting option values¶

All options and their values, when they are strings, are forced to be lower case. The values of an options class can be set and accessed by calling the class or by treating the class as an array.

Continuing the example from Construction of options classes:

sage: Menu.options
- dessert: espresso
- entree:  soup
- main:    pizza
- tip:     10
espresso
cake


Note that, provided there is no ambiguity, options and their values can be abbreviated:

sage: Menu.options('d')
'cake'
sage: Menu.options('m','t',des='esp', ent='sou')  # get and set several values at once
['pizza', 10]
15
15
- dessert: cake
- entree:  soup
- main:    pizza
- tip:     15
Traceback (most recent call last):
...
ValueError: P is not a valid value for main in the options for menu


## Setter functions¶

Each option of a GlobalOptions can be equipped with an optional setter function which is called after the value of the option is changed. In the following example, setting the option ‘add’ changes the state of the class by setting an attribute in this class using a classmethod(). Note that the options object is inserted after the creation of the class in order to access the classmethod() as A.setter:

sage: from sage.structure.global_options import GlobalOptions
sage: class A(SageObject):
....:     state = 0
....:     @classmethod
....:     def setter(cls, option, val):
....:         cls.state += int(val)
sage: class options(GlobalOptions):
....:     NAME = "A"
....:                checker=lambda v: int(v)>0,
....:                description='An option with a setter',
....:                setter=A.setter)
sage: A.options = options
sage: A.options
Current options for A
sage: a = A(); a.state
1
sage: a.options()
Current options for A
sage: a.state
5
sage: a.options()
Current options for A


## Documentation for options¶

The documentation for a GlobalOptions is automatically generated from the supplied options. For example, the generated documentation for the options menu defined in Construction of options classes is the following:

Fancy documentation
-------------------

OPTIONS:

- appetizer -- alternative name for entree
- dessert -- (default: espresso)
Dessert

- cake     -- waist begins again
- cream    -- fluffy, white stuff
- espresso -- life begins again

- entree -- (default: soup)
The first course of a meal

- bread -- oven baked
- rye   -- alias for bread
- soup  -- soup of the day

- main -- (default: pizza)
Main meal

- pasta -- penne arrabiata
- pizza -- thick crust

- tip -- (default: 10)
Reward for good service

The END!

See :class:~sage.structure.global_options.GlobalOptions for more features of these options.


In addition, help on each option, and its list of possible values, can be obtained by (trying to) set the option equal to ‘?’:

sage: Menu.options.dessert?                # not tested
- dessert -- (default: espresso)
Dessert

- cake     -- waist begins again
- cream    -- fluffy, white stuff
- espresso -- life begins again


## Dispatchers¶

The whole idea of a GlobalOptions class is that the options change the default behaviour of the associated classes. This can be done either by simply checking what the current value of the relevant option is. Another possibility is to use the options class as a dispatcher to associated methods. To use the dispatcher feature of a GlobalOptions class it is necessary to implement separate methods for each value of the option where the naming convention for these methods is that they start with a common prefix and finish with the value of the option.

If the value of a dispatchable option is set equal to a (user defined) function then this function is called instead of a class method.

For example, the options MyOptions can be used to dispatch the _repr_ method of the associated class MyClass as follows:

class MyClass(...):
def _repr_(self):
return self.options._dispatch(self,'_repr_','first_option')
def _repr_with_bells(self):
print('Bell!')
def _repr_with_whistles(self):
print('Whistles!')
class MyOptions(GlobalOptions):
...


In this example, first_option is an option of MyOptions which takes values bells, whistles, and so on. Note that it is necessary to make self, which is an instance of MyClass, an argument of the dispatcher because _dispatch() is a method of GlobalOptions and not a method of MyClass. Apart from MyOptions, as it is a method of this class, the arguments are the attached class (here MyClass), the prefix of the method of MyClass being dispatched, the option of MyOptions which controls the dispatching. All other arguments are passed through to the corresponding methods of MyClass. In general, a dispatcher is invoked as:

self.options._dispatch(self, dispatch_to, option, *args, **kargs)


Usually this will result in the method dispatch_to + '_' + MyOptions(options) of self being called with arguments *args and **kargs (if dispatch_to[-1] == '_' then the method dispatch_to + MyOptions(options) is called).

If MyOptions(options) is itself a function then the dispatcher will call this function instead. In this way, it is possible to allow the user to customise the default behaviour of this method. See _dispatch() for an example of how this can be achieved.

The dispatching capabilities of GlobalOptions allows options to be applied automatically without needing to parse different values of the option (the cost is that there must be a method for each value). The dispatching capabilities can also be used to make one option control several methods:

def __le__(self, other):
return self.options._dispatch(self, '_le_','cmp', other)
def __ge__(self, other):
return self.options._dispatch(self, '_ge_','cmp', other)
def _le_option_a(self, other):
return ...
def _ge_option_a(self, other):
return ...
def _le_option_b(self, other):
return ...
def _ge_option_b(self, other):
return ...


See _dispatch() for more details.

## Doc testing¶

All of the options and their effects should be doc-tested. However, in order not to break other tests, all options should be returned to their default state at the end of each test. To make this easier, every GlobalOptions class has a _reset() method for doing exactly this.

## Pickling¶

Options classes can only be pickled if they are the options for some standard sage class. In this case the class is specified using the arguments to GlobalOptions. For example options() is defined as:

class Partitions(UniqueRepresentation, Parent):
...
class options(GlobalOptions):
NAME = 'Partitions'
module = 'sage.combinat.partition'
...


Here is an example to test the pickling of a GlobalOptions instance:

sage: TestSuite(Partitions.options).run()

sage: print(Menu.options.dessert.__doc__)
- dessert -- (default: espresso)
Dessert

- cake     -- waist begins again
- cream    -- fluffy, white stuff
- espresso -- life begins again


AUTHORS:

• Andrew Mathas (2013): initial version
• Andrew Mathas (2016): overhaul making the options attributes, enabling
pickling and attaching the options to a class.
• Jeroen Demeyer (2017): use subclassing to create instances
class sage.structure.global_options.GlobalOptions(NAME=None, module='', option_class='', doc='', end_doc='', **options)

Bases: object

The GlobalOptions class is a generic class for setting and accessing global options for Sage objects.

While it is possible to create instances of GlobalOptions the usual way, the recommended syntax is to subclass from GlobalOptions. Thanks to some metaclass magic, this actually creates an instance of GlobalOptions instead of a subclass.

INPUT (as “attributes” of the class):

• NAME – specifies a name for the options class (optional; default: class name)
• module – gives the module that contains the associated options class
• option_class – gives the name of the associated module class (default: NAME)
• option = dict(...) – dictionary specifying an option

The options are specified by keyword arguments with their values being a dictionary which describes the option. The allowed/expected keys in the dictionary are:

• alias – defines alias/synonym for option values
• alt_name – alternative name for an option
• checker – a function for checking whether a particular value for the option is valid
• default – the default value of the option
• description – documentation string
• link_to – links to an option for this set of options to an option in another GlobalOptions
• setter – a function (class method) which is called whenever this option changes
• values – a dictionary of the legal values for this option (this automatically defines the corresponding checker); this dictionary gives the possible options, as keys, together with a brief description of them
• case_sensitive – (default: True) True or False depending on whether the values of the option are case sensitive

Options and their values can be abbreviated provided that this abbreviation is a prefix of a unique option.

EXAMPLES:

sage: from sage.structure.global_options import GlobalOptions
....:     class options(GlobalOptions):
....:         '''
....:         Fancy documentation
....:         -------------------
....:
....:         @[email protected]
....:
....:         End of Fancy documentation
....:         '''
....:         entree = dict(default='soup',
....:                     description='The first course of a meal',
....:                     values=dict(soup='soup of the day', bread='oven baked'),
....:         appetizer = dict(alt_name='entree')
....:         main = dict(default='pizza', description='Main meal',
....:                   values=dict(pizza='thick crust', pasta='penne arrabiata'),
....:                   case_sensitive=False)
....:         dessert = dict(default='espresso', description='Dessert',
....:                      values=dict(espresso='life begins again',
....:                                  cake='waist begins again',
....:                                  cream='fluffy white stuff'))
....:         tip = dict(default=10, description='Reward for good service',
....:                  checker=lambda tip: tip in range(0,20))
- dessert: espresso
- entree:  soup
- main:    pizza
- tip:     10
sage: Menu.options(entree='s')         # unambiguous abbreviations are allowed
(15, 15)
- dessert: espresso
- entree:  soup
- main:    pizza
- tip:     15
- dessert: espresso
- entree:  soup
- main:    pizza
- tip:     10
Traceback (most recent call last):
...
ValueError: 40 is not a valid value for tip in the options for menu
sage: Menu.options(m='p')           # ambiguous abbreviations are not allowed
Traceback (most recent call last):
...
ValueError: p is not a valid value for main in the options for menu


The documentation for the options class is automatically generated from the information which specifies the options:

Fancy documentation
-------------------

OPTIONS:

- dessert:  (default: espresso)
Dessert

- cake     -- waist begins again
- cream    -- fluffy white stuff
- espresso -- life begins again

- entree:  (default: soup)
The first course of a meal

- bread -- oven baked
- rye   -- alias for bread
- soup  -- soup of the day

- main:  (default: pizza)
Main meal

- pasta -- penne arrabiata
- pizza -- thick crust

- tip:  (default: 10)
Reward for good service

End of Fancy documentation

See :class:~sage.structure.global_options.GlobalOptions for more features of these options.


The possible values for an individual option can be obtained by (trying to) set it equal to ‘?’:

sage: Menu.options(des='?')
- dessert -- (default: espresso)
Dessert

- cake     -- waist begins again
- cream    -- fluffy white stuff
- espresso -- life begins again

Current value: espresso

default_value(*args, **kwds)

Deprecated: Use _default_value() instead. See trac ticket #18555 for details.

dispatch(*args, **kwds)

Deprecated: Use _dispatch() instead. See trac ticket #18555 for details.

reset(*args, **kwds)

Deprecated: Use _reset() instead. See trac ticket #18555 for details.

class sage.structure.global_options.GlobalOptionsMeta

Bases: type

Metaclass for GlobalOptions

This class is itself an instance of GlobalOptionsMetaMeta, which implements the subclass magic.

class sage.structure.global_options.GlobalOptionsMetaMeta

Bases: type

class sage.structure.global_options.Option(options, name)

Bases: object

An option.

Each option for an options class is an instance of this class which implements the magic that allows the options to the attributes of the options class that can be looked up, set and called.

By way of example, this class implements the following functionality.

EXAMPLES:

sage: Partitions.options.display
list
sage: Partitions.options.display='compact'
sage: Partitions.options.display('list')
sage: Partitions.options._reset()