#------------------------------------------------------------------------------
# Copyright (c) 2013-2019, Nucleic Development Team.
#
# Distributed under the terms of the Modified BSD License.
#
# The full license is in the file COPYING.txt, distributed with this software.
#------------------------------------------------------------------------------
from .catom import Member, GetAttr, SetAttr, DelAttr, reset_property
class Property(Member):
""" A Member which behaves similar to a Python property.
"""
__slots__ = ()
def __init__(self, fget=None, fset=None, fdel=None, cached=False):
""" Initialize a Property member.
Parameters
----------
fget : callable or None, optional
The callable invoked to get the property value. It must
accept a single argument which is the owner object. If not
provided, the property cannot be read. The default is None.
fset : callable or None, optional
The callable invoked to set the property value. It must
accept two arguments: the owner object and property value.
If not provided, the property cannot be set. The default
is None.
fdel : callable or None, optional
The callable invoked to delete the property value. It must
accept a single argument which is the owner object. If not
provided, the property cannot be deleted. The default is
None.
cached : bool, optional
Whether or not the property caches the computed value. A
cached property will only evaluate 'fget' once until the
'reset' method of the property is invoked. The default is
False.
"""
gm = GetAttr.CachedProperty if cached else GetAttr.Property
self.set_getattr_mode(gm, fget)
if cached and fset is not None:
raise ValueError('Cached property are read-only, but a setter was '
'specified.')
self.set_setattr_mode(SetAttr.Property, fset)
self.set_delattr_mode(DelAttr.Property, fdel)
@property
def fget(self):
""" Get the getter function for the property.
This will not find a specially named _get_* function.
"""
return self.getattr_mode[1]
@property
def fset(self):
""" Get the setter function for the property.
This will not find a specially named _set_* function.
"""
return self.setattr_mode[1]
@property
def fdel(self):
""" Get the deleter function for the property.
This will not find a specially named _del_* function.
"""
return self.delattr_mode[1]
@property
def cached(self):
""" Test whether or not this is a cached property.
"""
return self.getattr_mode[0] == GetAttr.CachedProperty
def getter(self, func):
""" Use the given function as the property getter.
This method is intended to be used as a decorator. The original
function will still be callable.
"""
mode, ignored = self.getattr_mode
self.set_getattr_mode(mode, func)
return func
def setter(self, func):
""" Use the given function as the property setter.
This method is intended to be used as a decorator. The original
function will still be callable.
"""
if self.cached:
raise ValueError('Cached property are read-only, but a setter was '
'specified.')
self.set_setattr_mode(SetAttr.Property, func)
return func
def deleter(self, func):
""" Use the given function as the property deleter.
This method is intended to be used as a decorator. The original
function will still be callable.
"""
self.set_delattr_mode(DelAttr.Property, func)
return func
def reset(self, owner):
""" Reset the value of the property.
The old property value will be cleared and the notifiers will
be run if the new value is different from the old value. If
the property is not cached, notifiers will be unconditionally
run using None as the old value.
"""
reset_property(self, owner)
def cached_property(fget):
""" A decorator which converts a function into a cached Property.
Parameters
----------
fget : callable
The callable invoked to get the property value. It must accept
a single argument which is the owner object.
"""
return Property(fget, cached=True)