Struct

class mosaic.types.struct.Struct(content=None, extensible=False, mutable=True)

Bases: mosaic.types.immutable.ImmutableObject

Structs represent dictionary-like objects that provide some extra features over Python’s OrderedDict.

Their internal representation is an OrderedDict, a dictionary that maintains the order in which members were added to it. Unlike traditional Python dicts, however, both square-bracket and dot notation are allowed to access the members of the Struct.

Structs can be extensible and mutable, which is determined when they are instantiated and remains unchanged for the life of the object.

When a Struct is not mutable, its members can only be assigned once, any further attempts at modifying the value of a member will result in an AttributeError. For mutable Structs the values of its members can be changed as many times as needed.

Whether or not a Struct is extensible affects how its members are accessed. When trying to find a member of the Struct, a naive search is performed first, assuming that the item exists within its internal dictionary.

If the search fails, and the Struct is not extensible an AttributeError is raised. Otherwise, a new search starts for members in the dictionary with a similar signature to the requested item.

If this search fails, an AttributeError is raised. If if does not fail and a match is found, the match is returned wrapped in a function that will evaluate whether the variant exists and is callable.

Parameters

• content (dict-like, optional) – Dict-like object to initialise the Struct, defaults to empty.

• extensible (bool, optional) – Whether or not the Struct should be extensible, defaults to False.

• mutable (bool, optional) – Whether or not the Struct should be mutable, defaults to True.

Examples

Let’s create an empty, immutable Struct:

>>> struct = Struct(mutable=False)
>>> struct.member = 10
>>> struct.member
10
>>> struct['member']
10
>>> struct.member = 20
AttributeError('The attribute member already exists in the container, this container is not mutable')

If the container was mutable instead:

>>> struct = Struct()
>>> struct.member = 10
>>> struct.member
10
>>> struct.member = 20
>>> struct.member
20

The same way mutability affects member assignment, extensibility affects how the members of the Struct are accessed:

>>> def function_variant_1():
>>>     print('Executed variant_1')
>>>
>>> def function_variant_2():
>>>     print('Executed variant_2')
>>>
>>> class KlassVariant1:
>>>     def __init__(self):
>>>         print('Instantiated Variant1')
>>>
>>> class KlassVariant2:
>>>     def __init__(self):
>>>         print('Instantiated Variant2')
>>>
>>> struct = Struct(extensible=True)
>>> struct.function_variant_1 = function_variant_1
>>> struct.function_variant_2 = function_variant_2
>>> struct.KlassVariant1 = KlassVariant1
>>> struct.KlassVariant2 = KlassVariant2
>>>
>>> struct.function(use='variant_1')
Executed variant_1
>>> struct.Klass('Variant2')()
Instantiated Variant2
>>> struct.Klass('variant_1')()
Instantiated Variant1

copy()

Returns a deepcopy of the Struct.

Returns

Copied Struct

Return type

Struct

delete(item)

Delete an item from the container using its key.

Parameters

item (str) – Name of the item to delete.

get(item, default=None)

Returns an item from the Struct or a default value if it is not found.

Parameters

• item (str) – Name of the item to find

• default (object, optional) – Default value to be returned in case the item is not found, defaults to None

items()

Returns the list of keys and values in the Struct.

Returns

List of keys and values in the Struct.

Return type

odict_items

keys()

Returns the list of keys in the Struct.

Returns

List of keys in the Struct.

Return type

odict_keys

pop(item, default=None)

Returns an item from the Struct and deletes it, or returns a default value if it is not found.

Parameters

• item (str) – Name of the item to find

• default (object, optional) – Default value to be returned in case the item is not found

update(content)

Updates the Struct with the contents of a dict-like object.

Parameters

content (dict-like) – Content with which to update the Struct

values()

Returns the list of values in the Struct.

Returns

List of values in the Struct.

Return type

odict_values