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"""Custom trait types."""
import inspect
from ast import literal_eval
from traitlets import Any, ClassBasedTraitType, TraitError, Undefined
from traitlets.utils.descriptions import describe
class TypeFromClasses(ClassBasedTraitType): # type:ignore[type-arg]
"""A trait whose value must be a subclass of a class in a specified list of classes."""
default_value: Any
def __init__(self, default_value=Undefined, klasses=None, **kwargs):
"""Construct a Type trait
A Type trait specifies that its values must be subclasses of
a class in a list of possible classes.
If only ``default_value`` is given, it is used for the ``klasses`` as
well. If neither are given, both default to ``object``.
Parameters
----------
default_value : class, str or None
The default value must be a subclass of klass. If an str,
the str must be a fully specified class name, like 'foo.bar.Bah'.
The string is resolved into real class, when the parent
:class:`HasTraits` class is instantiated.
klasses : list of class, str [ default object ]
Values of this trait must be a subclass of klass. The klass
may be specified in a string like: 'foo.bar.MyClass'.
The string is resolved into real class, when the parent
:class:`HasTraits` class is instantiated.
allow_none : bool [ default False ]
Indicates whether None is allowed as an assignable value.
"""
if default_value is Undefined:
new_default_value = object if (klasses is None) else klasses
else:
new_default_value = default_value
if klasses is None:
if (default_value is None) or (default_value is Undefined):
klasses = [object]
else:
klasses = [default_value]
# OneOfType requires a list of klasses to be specified (different than Type).
if not isinstance(klasses, (list, tuple, set)):
msg = "`klasses` must be a list of class names (type is str) or classes."
raise TraitError(msg)
for klass in klasses:
if not (inspect.isclass(klass) or isinstance(klass, str)):
msg = "A OneOfType trait must specify a list of classes."
raise TraitError(msg)
# Store classes.
self.klasses = klasses
super().__init__(new_default_value, **kwargs)
def subclass_from_klasses(self, value):
"""Check that a given class is a subclasses found in the klasses list."""
return any(issubclass(value, klass) for klass in self.importable_klasses)
def validate(self, obj, value):
"""Validates that the value is a valid object instance."""
if isinstance(value, str):
try:
value = self._resolve_string(value)
except ImportError as e:
emsg = (
f"The '{self.name}' trait of {obj} instance must be a type, but "
f"{value!r} could not be imported"
)
raise TraitError(emsg) from e
try:
if self.subclass_from_klasses(value):
return value
except Exception:
pass
self.error(obj, value)
def info(self):
"""Returns a description of the trait."""
result = "a subclass of "
for klass in self.klasses:
if not isinstance(klass, str):
klass = klass.__module__ + "." + klass.__name__ # noqa: PLW2901
result += f"{klass} or "
# Strip the last "or"
result = result.strip(" or ") # noqa: B005
if self.allow_none:
return result + " or None"
return result
def instance_init(self, obj):
"""Initialize an instance."""
self._resolve_classes()
super().instance_init(obj)
def _resolve_classes(self):
"""Resolve all string names to actual classes."""
self.importable_klasses = []
for klass in self.klasses:
if isinstance(klass, str):
# Try importing the classes to compare. Silently, ignore if not importable.
try:
klass = self._resolve_string(klass) # noqa: PLW2901
self.importable_klasses.append(klass)
except Exception:
pass
else:
self.importable_klasses.append(klass)
if isinstance(self.default_value, str):
self.default_value = self._resolve_string(self.default_value) # type:ignore[arg-type]
def default_value_repr(self):
"""The default value repr."""
value = self.default_value
if isinstance(value, str):
return repr(value)
else:
return repr(f"{value.__module__}.{value.__name__}")
class InstanceFromClasses(ClassBasedTraitType): # type:ignore[type-arg]
"""A trait whose value must be an instance of a class in a specified list of classes.
The value can also be an instance of a subclass of the specified classes.
Subclasses can declare default classes by overriding the klass attribute
"""
def __init__(self, klasses=None, args=None, kw=None, **kwargs):
"""Construct an Instance trait.
This trait allows values that are instances of a particular
class or its subclasses. Our implementation is quite different
from that of enthough.traits as we don't allow instances to be used
for klass and we handle the ``args`` and ``kw`` arguments differently.
Parameters
----------
klasses : list of classes or class_names (str)
The class that forms the basis for the trait. Class names
can also be specified as strings, like 'foo.bar.Bar'.
args : tuple
Positional arguments for generating the default value.
kw : dict
Keyword arguments for generating the default value.
allow_none : bool [ default False ]
Indicates whether None is allowed as a value.
Notes
-----
If both ``args`` and ``kw`` are None, then the default value is None.
If ``args`` is a tuple and ``kw`` is a dict, then the default is
created as ``klass(*args, **kw)``. If exactly one of ``args`` or ``kw`` is
None, the None is replaced by ``()`` or ``{}``, respectively.
"""
# If class
if klasses is None: # noqa: SIM114
self.klasses = klasses
# Verify all elements are either classes or strings.
elif all(inspect.isclass(k) or isinstance(k, str) for k in klasses):
self.klasses = klasses
else:
raise TraitError(
"The klasses attribute must be a list of class names or classes"
" not: %r" % klasses
)
if (kw is not None) and not isinstance(kw, dict):
msg = "The 'kw' argument must be a dict or None."
raise TraitError(msg)
if (args is not None) and not isinstance(args, tuple):
msg = "The 'args' argument must be a tuple or None."
raise TraitError(msg)
self.default_args = args
self.default_kwargs = kw
super().__init__(**kwargs)
def instance_from_importable_klasses(self, value):
"""Check that a given class is a subclasses found in the klasses list."""
return any(isinstance(value, klass) for klass in self.importable_klasses)
def validate(self, obj, value):
"""Validate an instance."""
if self.instance_from_importable_klasses(value):
return value
else:
self.error(obj, value)
def info(self):
"""Get the trait info."""
result = "an instance of "
assert self.klasses is not None
for klass in self.klasses:
if isinstance(klass, str):
result += klass
else:
result += describe("a", klass)
result += " or "
result = result.strip(" or ") # noqa: B005
if self.allow_none:
result += " or None"
return result
def instance_init(self, obj):
"""Initialize the trait."""
self._resolve_classes()
super().instance_init(obj)
def _resolve_classes(self):
"""Resolve all string names to actual classes."""
self.importable_klasses = []
assert self.klasses is not None
for klass in self.klasses:
if isinstance(klass, str):
# Try importing the classes to compare. Silently, ignore if not importable.
try:
klass = self._resolve_string(klass) # noqa: PLW2901
self.importable_klasses.append(klass)
except Exception:
pass
else:
self.importable_klasses.append(klass)
def make_dynamic_default(self):
"""Make the dynamic default for the trait."""
if (self.default_args is None) and (self.default_kwargs is None):
return None
return self.klass( # type:ignore[attr-defined]
*(self.default_args or ()), **(self.default_kwargs or {})
)
def default_value_repr(self):
"""Get the default value repr."""
return repr(self.make_dynamic_default())
def from_string(self, s):
"""Convert from a string."""
return literal_eval(s)
|
