candv.core._LazyConstantsGroup._evaluate() - Code Metrics - Inspection of "Tidy up and refactor the package" - oblalex/candv - Measure and Improve Code Quality continuously with Scrutinizer

Passed

Branch — master (9e8f7a)

by Oleksandr

created 2020-10-30 18:58 UTC

candv.core._LazyConstantsGroup._evaluate() A

↳ Parent: candv.core

Complexity

Conditions

Size

Total Lines	19
Code Lines	15

Duplication

Lines	0
Ratio	0 %

Importance

Changes

Metric	Value
eloc	15
dl	0
loc	19
rs	9.65
c	0
b	0
f	0
cc	1
nop	3

"""
Defines base constant and base container for constants.

"""
import types

from collections import OrderedDict as odict

from .exceptions import CandvConstantAlreadyBoundError
from .exceptions import CandvContainerMisusedError
from .exceptions import CandvInvalidConstantClass
from .exceptions import CandvInvalidGroupMemberError
from .exceptions import CandvMissingConstantError

from .utils import export


UNBOUND_CONSTANT_CONTAINER_NAME = "__UNBOUND__"


@export
class SimpleConstant:
  """
  Base class for all constants.

  :ivar str name:
    constant's name: set up automatically and is equal to the name of the
    container's attribute

  """

  def __init__(self):
    self.name = None
    self.container = None

  def _post_init(self, name, container=None):
    """
    Called automatically by the container after container's class construction.

    """
    self.name = name
    self.container = container

  def to_group(self, group_class, **group_members):
    """
    Convert a constant into a constants group.

    :param class group_class:
      a class of group container which will be created

    :param group_members:
      unpacked dict which defines group members

    :returns:
      a lazy constants group which will be evaluated by the container.
      Method :meth:`merge_into_group` will be called during evaluation of the
      group

    **Example**:

    .. code-block:: python

      from candv import Constants
      from candv import SimpleConstant


      class FOO(Constants):
        A = SimpleConstant()
        B = SimpleConstant().to_group(Constants,

          B2 = SimpleConstant(),
          B0 = SimpleConstant(),
          B1 = SimpleConstant(),
        )

    """
    return _LazyConstantsGroup(self, group_class, **group_members)

  def merge_into_group(self, group):
    """
    Called automatically by the container after group construction.

    .. note::

      Redefine this method in all derived classes. Attach all custom attributes
      and methods to the group here.

    :param group:
      an instance of :class:`Constants` or of its subclass into which
      this constant will be merged

    :returns: ``None``

    """

  @property
  def full_name(self):
    prefix = (
      self.container.full_name
      if self.container
      else UNBOUND_CONSTANT_CONTAINER_NAME
    )
    return f"{prefix}.{self.name}"

  def to_primitive(self, context=None):
    """
    Represent the constant via Python's primitive data structures.

    .. versionadded:: 1.3.0

    """
    return {
      'name': self.name,
    }

  def __repr__(self):
    """
    Produce a text identifying the constant.

    """
    return f"<constant '{self.full_name}'>"

  def __hash__(self):
    """
    .. versionadded:: 1.3.1
    """
    return hash(self.full_name)

  def __eq__(self, other):
    """
    .. versionadded:: 1.3.1
    """
    return (
      isinstance(other, SimpleConstant)
      and (self.full_name == other.full_name)
    )

  def __ne__(self, other):
    """
    .. versionadded:: 1.3.1
    """
    return not (self == other)


class _LazyConstantsGroup:

  def __init__(self, constant, group_class, **group_members):
    self._validate_group_members(group_members)
    self.constant = constant
    self.group_class = group_class
    self.group_members = group_members

  @staticmethod
  def _validate_group_members(group_members):
    for name, obj in group_members.items():
      if not isinstance(obj, (SimpleConstant, _LazyConstantsGroup)):
        raise CandvInvalidGroupMemberError(
          f'invalid group member "{obj}": only instances of "{SimpleConstant}" '
          f'or other groups are allowed'
        )

  def _evaluate(self, parent, name):
    full_name = f"{parent.full_name}.{name}"
    group_bases = (self.group_class, )
    self.group_members.update({
      'name': name,
      'full_name': full_name,
      'container': parent,
      '__repr': f"<constants group '{full_name}'>",
    })

    group = type(full_name, group_bases, self.group_members)
    group.to_primitive = self._make_to_primitive(group, self.constant)
    self.constant.merge_into_group(group)

    del self.constant
    del self.group_class
    del self.group_members

    return group

  @staticmethod
  def _make_to_primitive(group, constant):
    # define aliases to avoid shadowing and infinite recursion
    constant_primitive = constant.to_primitive
    group_primitive = group.to_primitive

    def to_primitive(self, context=None):
      primitive = constant_primitive(context)
      primitive.update(group_primitive(context))
      return primitive

    return types.MethodType(to_primitive, group)


class _ConstantsContainerMeta(type):
  """
  Metaclass for creating container classes for constants.

  """
  def __new__(self, class_name, bases, attributes):
    self._ensure_attribute(attributes, "name", class_name)
    self._ensure_attribute(attributes, "full_name", class_name)

    cls = super().__new__(self, class_name, bases, attributes)

    # set before validations to get correct repr
    cls.__repr = self._get_or_make_repr_value(attributes)

    self._validate_constant_class(cls)

    cls._members = self._make_members_from_attributes(cls, attributes)

    return cls

  @staticmethod
  def _ensure_attribute(attributes, attribute_name, default_value):
    if attribute_name not in attributes:
      attributes[attribute_name] = default_value

  @staticmethod
  def _validate_constant_class(target_cls):
    constant_class = getattr(target_cls, "constant_class", None)

    if not issubclass(constant_class, SimpleConstant):
      raise CandvInvalidConstantClass(
        f'invalid "constant_class" for "{target_cls}": must be derived from '
        f'"{SimpleConstant}", but got "{constant_class}"'
      )

  @staticmethod
  def _get_or_make_repr_value(attributes):
    value = attributes.pop("__repr", None)

    if not value:
      name = attributes["name"]
      value = f"<constants container '{name}'>"

    return value

  @classmethod
  def _make_members_from_attributes(cls, target_cls, attributes):
    members = []

    for name, the_object in attributes.items():
      if isinstance(the_object, _LazyConstantsGroup):
        group = the_object._evaluate(target_cls, name)
        setattr(target_cls, name, group)
        members.append((name, group))

      elif isinstance(the_object, target_cls.constant_class):
        cls._validate_constant_is_not_bound(target_cls, name, the_object)
        the_object._post_init(name=name, container=target_cls)
        members.append((name, the_object))

      elif isinstance(the_object, SimpleConstant):
        # init but do not append constants which are more generic
        # than ``constant_class``
        the_object._post_init(name=name)

    return odict(members)

  @staticmethod
  def _validate_constant_is_not_bound(target_cls, attribute_name, the_object):
    if the_object.container is not None:
      raise CandvConstantAlreadyBoundError(
        f'cannot use "{the_object}" as value for "{attribute_name}" attribute '
        f'of "{target_cls}" container: already bound to "{the_object.container}"'
      )

  def __repr__(self):
    return self.__repr

  def __getitem__(self, name):
    """
    Try to get constant by its name.

    :param str name: name of constant to search for

    :returns: a constant
    :rtype: an instance of :class:`SimpleConstant` or its subclass

    :raises CandvMissingConstantError:
      if constant with name ``name`` is not present in container

    **Example**:

    .. code-block:: python

      from candv import Constants
      from candv import SimpleConstant


      class FOO(Constants):
        foo = SimpleConstant()
        bar = SimpleConstant()

    .. code-block:: python

      >>> FOO['foo']
      <constant 'FOO.foo'>

    """
    try:
      return self._members[name]
    except KeyError:
      raise CandvMissingConstantError(
        f'constant "{name}" is not present in "{self}"'
      )

  def __contains__(self, name):
    return name in self._members

  def __len__(self):
    return len(self._members)

  def __iter__(self):
    return self.iternames()

  def get(self, name, default=None):
    """
    Try to get a constant by its name or fallback to a default.

    :param str name:
      name of constant to search

    :param default:
      an object returned by default if constant with a given name is not present
      in the container

    :returns: a constant or a default value
    :rtype: an instance of :class:`SimpleConstant` or its subclass, or `default` value

    **Example**:

    .. code-block:: python

      from candv import Constants
      from candv import SimpleConstant


      class FOO(Constants):
        foo = SimpleConstant()
        bar = SimpleConstant()

    .. code-block:: python

      >>> FOO.get('foo')
      <constant 'FOO.foo'>

      >>> FOO.get('xxx')
      None

      >>> FOO.get('xxx', default=123)
      123

    """
    return self._members.get(name, default)

  def has_name(self, name):
    """
    Check if the container has a constant with a given name.

    :param str name: a constant's name to check

    :returns: ``True`` if given name belongs to container, ``False`` otherwise
    :rtype: :class:`bool`

    """
    return name in self

  def names(self):
    """
    List all names of constants within the container.

    :returns: a list of constant names in order constants were defined
    :rtype: :class:`list` of strings

    **Example**:

    .. code-block:: python

      from candv import Constants
      from candv import SimpleConstant


      class FOO(Constants):
        foo = SimpleConstant()
        bar = SimpleConstant()

    .. code-block:: python

      >>> FOO.names()
      ['foo', 'bar']

    """
    return list(self._members.keys())

  def iternames(self):
    """
    Get an iterator over constants names.

    Same as :meth:`names`, but returns an interator.

    """
    return iter(self._members.keys())

  def constants(self):
    """
    List all constants in the container.

    :returns: list of constants in order they were defined
    :rtype: :class:`list`

    **Example**:

    .. code-block:: python

      from candv import Constants
      from candv import SimpleConstant


      class FOO(Constants):
        foo = SimpleConstant()
        bar = SimpleConstant()

    .. code-block:: python

      >>> [x.name for x in FOO.constants()]
      ['foo', 'bar']

    """
    return list(self._members.values())

  def iterconstants(self):
    """
    Get an iterator over constants.

    Same as :meth:`constants`, but returns an interator

    """
    return iter(self._members.values())

  def items(self):
    """
    Get list of constants names along with constants themselves.

    :returns:
      list of constants with their names in order they were defined.
      Each element in the list is a :class:`tuple` in format ``(name, constant)``.
    :rtype: :class:`list`

    **Example**:

    .. code-block:: python

      from candv import Constants
      from candv import SimpleConstant

      class FOO(Constants):
        foo = SimpleConstant()
        bar = SimpleConstant()

    .. code-block:: python

      >>> FOO.items()
      [('foo', <constant 'FOO.foo'>), ('bar', <constant 'FOO.bar'>)]

    """
    return list(self._members.items())

  def iteritems(self):
    """
    Get an iterator over constants names along with constants themselves.

    Same as :meth:`items`, but returns an interator

    """
    return iter(self._members.items())

  #: .. versionadded:: 1.1.2
  #:
  #: Alias for :meth:`constants`.
  #: Added for consistency with dictionaries. Use :class:`~candv.Values` and
  #: :meth:`~candv.Values.values` if you need to have constants with real
  #: values.
  values = constants

  #: .. versionadded:: 1.1.2
  #:
  #: Alias for :meth:`iterconstants`.
  #: Added for consistency with dictionaries. Use :class:`~candv.Values` and
  #: :meth:`~candv.Values.itervalues` if you need to have constants with real
  #: values.
  itervalues = iterconstants

  def to_primitive(self, context=None):
    """
    .. versionadded:: 1.3.0
    """
    items = [
      x.to_primitive(context)
      for x in self.iterconstants()
    ]
    return {
      'name': self.name,
      'items': items,
    }


@export
class Constants(metaclass=_ConstantsContainerMeta):
  """
  Base class for creating constants containers.

  Each constant defined within the container will remember its creation order.

  See an example in :meth:`constants`.

  :cvar constant_class:
    defines a class of constants which a container will store.
    This attribute **MUST** be set up manually when you define a new container
    type. Otherwise container will not be initialized. Default: ``None``

  :raises CandvContainerMisusedError:
    if you try to create an instance of container. Containers are singletons and
    they cannot be instantiated. Their attributes must be used directly.

  """

  #: Defines a top-level class of constants which can be stored by container
  constant_class = SimpleConstant

  def __new__(cls):
    raise CandvContainerMisusedError(
      f'"{cls}" cannot be instantiated: constant containers are not designed '
      f'for that'
    )


@export
def with_constant_class(the_class):
  """
  Create a mixin class with ``constant_class`` attribute.

  Allows to set a constant class for constants container outside container itself.
  This may help to create more readable container definition, e.g.:

  .. code-block:: python

    from candv import Constants
    from candv import SimpleConstant
    from candv import with_constant_class


    class CustomConstant(SimpleConstant):
      ...

    class FOO(with_constant_class(CustomConstant), Constants):
      A = CustomConstant()
      B = CustomConstant()

  .. code-block:: python

    >>> FOO.constant_class
    <class '__main__.CustomConstant'>

  """
  class ConstantsMixin:
    constant_class = the_class

  return ConstantsMixin


1			"""
2			Defines base constant and base container for constants.
3
4			"""
5			import types
6
7			from collections import OrderedDict as odict
8
9			from .exceptions import CandvConstantAlreadyBoundError
10			from .exceptions import CandvContainerMisusedError
11			from .exceptions import CandvInvalidConstantClass
12			from .exceptions import CandvInvalidGroupMemberError
13			from .exceptions import CandvMissingConstantError
14
15			from .utils import export
16
17
18			UNBOUND_CONSTANT_CONTAINER_NAME = "__UNBOUND__"
19
20
21			@export
22			class SimpleConstant:
23			"""
24			Base class for all constants.
25
26			:ivar str name:
27			constant's name: set up automatically and is equal to the name of the
28			container's attribute
29
30			"""
31
32			def __init__(self):
33			self.name = None
34			self.container = None
35
36			def _post_init(self, name, container=None):
37			"""
38			Called automatically by the container after container's class construction.
39
40			"""
41			self.name = name
42			self.container = container
43
44			def to_group(self, group_class, **group_members):
45			"""
46			Convert a constant into a constants group.
47
48			:param class group_class:
49			a class of group container which will be created
50
51			:param group_members:
52			unpacked dict which defines group members
53
54			:returns:
55			a lazy constants group which will be evaluated by the container.
56			Method :meth:`merge_into_group` will be called during evaluation of the
57			group
58
59			Example:
60
61			.. code-block:: python
62
63			from candv import Constants
64			from candv import SimpleConstant
65
66
67			class FOO(Constants):
68			A = SimpleConstant()
69			B = SimpleConstant().to_group(Constants,
70
71			B2 = SimpleConstant(),
72			B0 = SimpleConstant(),
73			B1 = SimpleConstant(),
74			)
75
76			"""
77			return _LazyConstantsGroup(self, group_class, **group_members)
78
79			def merge_into_group(self, group):
80			"""
81			Called automatically by the container after group construction.
82
83			.. note::
84
85			Redefine this method in all derived classes. Attach all custom attributes
86			and methods to the group here.
87
88			:param group:
89			an instance of :class:`Constants` or of its subclass into which
90			this constant will be merged
91
92			:returns: ``None``
93
94			"""
95
96			@property
97			def full_name(self):
98			prefix = (
99			self.container.full_name
100			if self.container
101			else UNBOUND_CONSTANT_CONTAINER_NAME
102			)
103			return f"{prefix}.{self.name}"
104
105			def to_primitive(self, context=None):
106			"""
107			Represent the constant via Python's primitive data structures.
108
109			.. versionadded:: 1.3.0
110
111			"""
112			return {
113			'name': self.name,
114			}
115
116			def __repr__(self):
117			"""
118			Produce a text identifying the constant.
119
120			"""
121			return f"<constant '{self.full_name}'>"
122
123			def __hash__(self):
124			"""
125			.. versionadded:: 1.3.1
126			"""
127			return hash(self.full_name)
128
129			def __eq__(self, other):
130			"""
131			.. versionadded:: 1.3.1
132			"""
133			return (
134			isinstance(other, SimpleConstant)
135			and (self.full_name == other.full_name)
136			)
137
138			def __ne__(self, other):
139			"""
140			.. versionadded:: 1.3.1
141			"""
142			return not (self == other)
143
144
145			class _LazyConstantsGroup:
146
147			def __init__(self, constant, group_class, **group_members):
148			self._validate_group_members(group_members)
149			self.constant = constant
150			self.group_class = group_class
151			self.group_members = group_members
152
153			@staticmethod
154			def _validate_group_members(group_members):
155			for name, obj in group_members.items():
156			if not isinstance(obj, (SimpleConstant, _LazyConstantsGroup)):
157			raise CandvInvalidGroupMemberError(
158			f'invalid group member "{obj}": only instances of "{SimpleConstant}" '
159			f'or other groups are allowed'
160			)
161
162			def _evaluate(self, parent, name):
163			full_name = f"{parent.full_name}.{name}"
164			group_bases = (self.group_class, )
165			self.group_members.update({
166			'name': name,
167			'full_name': full_name,
168			'container': parent,
169			'__repr': f"<constants group '{full_name}'>",
170			})
171
172			group = type(full_name, group_bases, self.group_members)
173			group.to_primitive = self._make_to_primitive(group, self.constant)
174			self.constant.merge_into_group(group)
175
176			del self.constant
177			del self.group_class
178			del self.group_members
179
180			return group
181
182			@staticmethod
183			def _make_to_primitive(group, constant):
184			# define aliases to avoid shadowing and infinite recursion
185			constant_primitive = constant.to_primitive
186			group_primitive = group.to_primitive
187
188			def to_primitive(self, context=None):
189			primitive = constant_primitive(context)
190			primitive.update(group_primitive(context))
191			return primitive
192
193			return types.MethodType(to_primitive, group)
194
195
196			class _ConstantsContainerMeta(type):
197			"""
198			Metaclass for creating container classes for constants.
199
200			"""
201			def __new__(self, class_name, bases, attributes):
202			self._ensure_attribute(attributes, "name", class_name)
203			self._ensure_attribute(attributes, "full_name", class_name)
204
205			cls = super().__new__(self, class_name, bases, attributes)
206
207			# set before validations to get correct repr
208			cls.__repr = self._get_or_make_repr_value(attributes)
209
210			self._validate_constant_class(cls)
211
212			cls._members = self._make_members_from_attributes(cls, attributes)
213
214			return cls
215
216			@staticmethod
217			def _ensure_attribute(attributes, attribute_name, default_value):
218			if attribute_name not in attributes:
219			attributes[attribute_name] = default_value
220
221			@staticmethod
222			def _validate_constant_class(target_cls):
223			constant_class = getattr(target_cls, "constant_class", None)
224
225			if not issubclass(constant_class, SimpleConstant):
226			raise CandvInvalidConstantClass(
227			f'invalid "constant_class" for "{target_cls}": must be derived from '
228			f'"{SimpleConstant}", but got "{constant_class}"'
229			)
230
231			@staticmethod
232			def _get_or_make_repr_value(attributes):
233			value = attributes.pop("__repr", None)
234
235			if not value:
236			name = attributes["name"]
237			value = f"<constants container '{name}'>"
238
239			return value
240
241			@classmethod
242			def _make_members_from_attributes(cls, target_cls, attributes):
243			members = []
244
245			for name, the_object in attributes.items():
246			if isinstance(the_object, _LazyConstantsGroup):
247			group = the_object._evaluate(target_cls, name)
248			setattr(target_cls, name, group)
249			members.append((name, group))
250
251			elif isinstance(the_object, target_cls.constant_class):
252			cls._validate_constant_is_not_bound(target_cls, name, the_object)
253			the_object._post_init(name=name, container=target_cls)
254			members.append((name, the_object))
255
256			elif isinstance(the_object, SimpleConstant):
257			# init but do not append constants which are more generic
258			# than ``constant_class``
259			the_object._post_init(name=name)
260
261			return odict(members)
262
263			@staticmethod
264			def _validate_constant_is_not_bound(target_cls, attribute_name, the_object):
265			if the_object.container is not None:
266			raise CandvConstantAlreadyBoundError(
267			f'cannot use "{the_object}" as value for "{attribute_name}" attribute '
268			f'of "{target_cls}" container: already bound to "{the_object.container}"'
269			)
270
271			def __repr__(self):
272			return self.__repr
273
274			def __getitem__(self, name):
275			"""
276			Try to get constant by its name.
277
278			:param str name: name of constant to search for
279
280			:returns: a constant
281			:rtype: an instance of :class:`SimpleConstant` or its subclass
282
283			:raises CandvMissingConstantError:
284			if constant with name ``name`` is not present in container
285
286			Example:
287
288			.. code-block:: python
289
290			from candv import Constants
291			from candv import SimpleConstant
292
293
294			class FOO(Constants):
295			foo = SimpleConstant()
296			bar = SimpleConstant()
297
298			.. code-block:: python
299
300			>>> FOO['foo']
301			<constant 'FOO.foo'>
302
303			"""
304			try:
305			return self._members[name]
306			except KeyError:
307			raise CandvMissingConstantError(
308			f'constant "{name}" is not present in "{self}"'
309			)
310
311			def __contains__(self, name):
312			return name in self._members
313
314			def __len__(self):
315			return len(self._members)
316
317			def __iter__(self):
318			return self.iternames()
319
320			def get(self, name, default=None):
321			"""
322			Try to get a constant by its name or fallback to a default.
323
324			:param str name:
325			name of constant to search
326
327			:param default:
328			an object returned by default if constant with a given name is not present
329			in the container
330
331			:returns: a constant or a default value
332			:rtype: an instance of :class:`SimpleConstant` or its subclass, or `default` value
333
334			Example:
335
336			.. code-block:: python
337
338			from candv import Constants
339			from candv import SimpleConstant
340
341
342			class FOO(Constants):
343			foo = SimpleConstant()
344			bar = SimpleConstant()
345
346			.. code-block:: python
347
348			>>> FOO.get('foo')
349			<constant 'FOO.foo'>
350
351			>>> FOO.get('xxx')
352			None
353
354			>>> FOO.get('xxx', default=123)
355			123
356
357			"""
358			return self._members.get(name, default)
359
360			def has_name(self, name):
361			"""
362			Check if the container has a constant with a given name.
363
364			:param str name: a constant's name to check
365
366			:returns: ``True`` if given name belongs to container, ``False`` otherwise
367			:rtype: :class:`bool`
368
369			"""
370			return name in self
371
372			def names(self):
373			"""
374			List all names of constants within the container.
375
376			:returns: a list of constant names in order constants were defined
377			:rtype: :class:`list` of strings
378
379			Example:
380
381			.. code-block:: python
382
383			from candv import Constants
384			from candv import SimpleConstant
385
386
387			class FOO(Constants):
388			foo = SimpleConstant()
389			bar = SimpleConstant()
390
391			.. code-block:: python
392
393			>>> FOO.names()
394			['foo', 'bar']
395
396			"""
397			return list(self._members.keys())
398
399			def iternames(self):
400			"""
401			Get an iterator over constants names.
402
403			Same as :meth:`names`, but returns an interator.
404
405			"""
406			return iter(self._members.keys())
407
408			def constants(self):
409			"""
410			List all constants in the container.
411
412			:returns: list of constants in order they were defined
413			:rtype: :class:`list`
414
415			Example:
416
417			.. code-block:: python
418
419			from candv import Constants
420			from candv import SimpleConstant
421
422
423			class FOO(Constants):
424			foo = SimpleConstant()
425			bar = SimpleConstant()
426
427			.. code-block:: python
428
429			>>> [x.name for x in FOO.constants()]
430			['foo', 'bar']
431
432			"""
433			return list(self._members.values())
434
435			def iterconstants(self):
436			"""
437			Get an iterator over constants.
438
439			Same as :meth:`constants`, but returns an interator
440
441			"""
442			return iter(self._members.values())
443
444			def items(self):
445			"""
446			Get list of constants names along with constants themselves.
447
448			:returns:
449			list of constants with their names in order they were defined.
450			Each element in the list is a :class:`tuple` in format ``(name, constant)``.
451			:rtype: :class:`list`
452
453			Example:
454
455			.. code-block:: python
456
457			from candv import Constants
458			from candv import SimpleConstant
459
460			class FOO(Constants):
461			foo = SimpleConstant()
462			bar = SimpleConstant()
463
464			.. code-block:: python
465
466			>>> FOO.items()
467			[('foo', <constant 'FOO.foo'>), ('bar', <constant 'FOO.bar'>)]
468
469			"""
470			return list(self._members.items())
471
472			def iteritems(self):
473			"""
474			Get an iterator over constants names along with constants themselves.
475
476			Same as :meth:`items`, but returns an interator
477
478			"""
479			return iter(self._members.items())
480
481			#: .. versionadded:: 1.1.2
482			#:
483			#: Alias for :meth:`constants`.
484			#: Added for consistency with dictionaries. Use :class:`~candv.Values` and
485			#: :meth:`~candv.Values.values` if you need to have constants with real
486			#: values.
487			values = constants
488
489			#: .. versionadded:: 1.1.2
490			#:
491			#: Alias for :meth:`iterconstants`.
492			#: Added for consistency with dictionaries. Use :class:`~candv.Values` and
493			#: :meth:`~candv.Values.itervalues` if you need to have constants with real
494			#: values.
495			itervalues = iterconstants
496
497			def to_primitive(self, context=None):
498			"""
499			.. versionadded:: 1.3.0
500			"""
501			items = [
502			x.to_primitive(context)
503			for x in self.iterconstants()
504			]
505			return {
506			'name': self.name,
507			'items': items,
508			}
509
510
511			@export
512			class Constants(metaclass=_ConstantsContainerMeta):
513			"""
514			Base class for creating constants containers.
515
516			Each constant defined within the container will remember its creation order.
517
518			See an example in :meth:`constants`.
519
520			:cvar constant_class:
521			defines a class of constants which a container will store.
522			This attribute MUST be set up manually when you define a new container
523			type. Otherwise container will not be initialized. Default: ``None``
524
525			:raises CandvContainerMisusedError:
526			if you try to create an instance of container. Containers are singletons and
527			they cannot be instantiated. Their attributes must be used directly.
528
529			"""
530
531			#: Defines a top-level class of constants which can be stored by container
532			constant_class = SimpleConstant
533
534			def __new__(cls):
535			raise CandvContainerMisusedError(
536			f'"{cls}" cannot be instantiated: constant containers are not designed '
537			f'for that'
538			)
539
540
541			@export
542			def with_constant_class(the_class):
543			"""
544			Create a mixin class with ``constant_class`` attribute.
545
546			Allows to set a constant class for constants container outside container itself.
547			This may help to create more readable container definition, e.g.:
548
549			.. code-block:: python
550
551			from candv import Constants
552			from candv import SimpleConstant
553			from candv import with_constant_class
554
555
556			class CustomConstant(SimpleConstant):
557			...
558
559			class FOO(with_constant_class(CustomConstant), Constants):
560			A = CustomConstant()
561			B = CustomConstant()
562
563			.. code-block:: python
564
565			>>> FOO.constant_class
566			<class '__main__.CustomConstant'>
567
568			"""
569			class ConstantsMixin:
570			constant_class = the_class
571
572			return ConstantsMixin
573

oblalex / candv

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candv.core._LazyConstantsGroup._evaluate() A

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