/usr/share/pyshared/louie/saferef.py is in python-louie 1.1-2.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 | """Refactored 'safe reference from dispatcher.py"""
import weakref
import traceback
def safe_ref(target, on_delete=None):
"""Return a *safe* weak reference to a callable target.
- ``target``: The object to be weakly referenced, if it's a bound
method reference, will create a BoundMethodWeakref, otherwise
creates a simple weakref.
- ``on_delete``: If provided, will have a hard reference stored to
the callable to be called after the safe reference goes out of
scope with the reference object, (either a weakref or a
BoundMethodWeakref) as argument.
"""
if hasattr(target, 'im_self'):
if target.im_self is not None:
# Turn a bound method into a BoundMethodWeakref instance.
# Keep track of these instances for lookup by disconnect().
assert hasattr(target, 'im_func'), (
"safe_ref target %r has im_self, but no im_func, "
"don't know how to create reference"
% target
)
reference = BoundMethodWeakref(target=target, on_delete=on_delete)
return reference
if callable(on_delete):
return weakref.ref(target, on_delete)
else:
return weakref.ref(target)
class BoundMethodWeakref(object):
"""'Safe' and reusable weak references to instance methods.
BoundMethodWeakref objects provide a mechanism for referencing a
bound method without requiring that the method object itself
(which is normally a transient object) is kept alive. Instead,
the BoundMethodWeakref object keeps weak references to both the
object and the function which together define the instance method.
Attributes:
- ``key``: The identity key for the reference, calculated by the
class's calculate_key method applied to the target instance method.
- ``deletion_methods``: Sequence of callable objects taking single
argument, a reference to this object which will be called when
*either* the target object or target function is garbage
collected (i.e. when this object becomes invalid). These are
specified as the on_delete parameters of safe_ref calls.
- ``weak_self``: Weak reference to the target object.
- ``weak_func``: Weak reference to the target function.
Class Attributes:
- ``_all_instances``: Class attribute pointing to all live
BoundMethodWeakref objects indexed by the class's
calculate_key(target) method applied to the target objects.
This weak value dictionary is used to short-circuit creation so
that multiple references to the same (object, function) pair
produce the same BoundMethodWeakref instance.
"""
_all_instances = weakref.WeakValueDictionary()
def __new__(cls, target, on_delete=None, *arguments, **named):
"""Create new instance or return current instance.
Basically this method of construction allows us to
short-circuit creation of references to already- referenced
instance methods. The key corresponding to the target is
calculated, and if there is already an existing reference,
that is returned, with its deletion_methods attribute updated.
Otherwise the new instance is created and registered in the
table of already-referenced methods.
"""
key = cls.calculate_key(target)
current = cls._all_instances.get(key)
if current is not None:
current.deletion_methods.append(on_delete)
return current
else:
base = super(BoundMethodWeakref, cls).__new__(cls)
cls._all_instances[key] = base
base.__init__(target, on_delete, *arguments, **named)
return base
def __init__(self, target, on_delete=None):
"""Return a weak-reference-like instance for a bound method.
- ``target``: The instance-method target for the weak reference,
must have im_self and im_func attributes and be
reconstructable via the following, which is true of built-in
instance methods::
target.im_func.__get__( target.im_self )
- ``on_delete``: Optional callback which will be called when
this weak reference ceases to be valid (i.e. either the
object or the function is garbage collected). Should take a
single argument, which will be passed a pointer to this
object.
"""
def remove(weak, self=self):
"""Set self.isDead to True when method or instance is destroyed."""
methods = self.deletion_methods[:]
del self.deletion_methods[:]
try:
del self.__class__._all_instances[self.key]
except KeyError:
pass
for function in methods:
try:
if callable(function):
function(self)
except Exception:
try:
traceback.print_exc()
except AttributeError, e:
print ('Exception during saferef %s '
'cleanup function %s: %s' % (self, function, e))
self.deletion_methods = [on_delete]
self.key = self.calculate_key(target)
self.weak_self = weakref.ref(target.im_self, remove)
self.weak_func = weakref.ref(target.im_func, remove)
self.self_name = str(target.im_self)
self.func_name = str(target.im_func.__name__)
def calculate_key(cls, target):
"""Calculate the reference key for this reference.
Currently this is a two-tuple of the id()'s of the target
object and the target function respectively.
"""
return (id(target.im_self), id(target.im_func))
calculate_key = classmethod(calculate_key)
def __str__(self):
"""Give a friendly representation of the object."""
return "%s(%s.%s)" % (
self.__class__.__name__,
self.self_name,
self.func_name,
)
__repr__ = __str__
def __nonzero__(self):
"""Whether we are still a valid reference."""
return self() is not None
def __cmp__(self, other):
"""Compare with another reference."""
if not isinstance(other, self.__class__):
return cmp(self.__class__, type(other))
return cmp(self.key, other.key)
def __call__(self):
"""Return a strong reference to the bound method.
If the target cannot be retrieved, then will return None,
otherwise returns a bound instance method for our object and
function.
Note: You may call this method any number of times, as it does
not invalidate the reference.
"""
target = self.weak_self()
if target is not None:
function = self.weak_func()
if function is not None:
return function.__get__(target)
return None
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