qtils.properties module

See more usage examples in Property decorators

qtils.properties.weakproperty(setter)

Returns a property that stores values as weakref.Ref()

The weakref object is stored as '_' + setter.__name__

Parameters:setter (function) – setter function (can be an empty function) Returns:returns property instance

Example

>>> import sys
>>> class SomeClass(object): pass
>>> class Foo(object):
...     @weakproperty
...     def bar(self, value): pass
...
>>> some_obj = SomeClass()
>>> original_refcount = sys.getrefcount(some_obj)
>>> foo = Foo()
>>> foo.bar = some_obj  # Reference count should not increase because some_obj is weak referenced.
>>> original_refcount == sys.getrefcount(some_obj)
True
>>> foo._bar # weakref object stored as private variable
<weakref at ... to 'SomeClass' at ...>
>>> foo.bar
<qtils.properties.SomeClass object at ...>
>>> foo.bar == some_obj
True

qtils.properties.cachedproperty(getter=None, setter=None, deleter=None, varname=None)

Returns a property that caches first return of getter until a del is called.

Parameters:

• getter (function) – Getter function
• setter (function) – Setter function
• deleter (function) – Deleter function
• varname (str) – Variable name to store cached data at, defaults to getter.__name__

Returns:

property object with caching ability

Return type:

return (property)

Example

Tyical usage:

>>> class Foo(object):
...     @cachedproperty
...     def bar(self):
...         # doing some super computation-intensive thing here
...         print('getter called')
...         return "hello world"
...
>>> obj = Foo()
>>> obj.bar         # first call, getter is called
getter called
'hello world'
>>> obj.bar         # second call, getter is not called
'hello world'
>>> obj._bar        # data is stored under '_'+setter.__name__
'hello world'
>>> del obj.bar     # removing cached value
>>> obj.bar         # getter is called again
getter called
'hello world'
>>> del obj.bar
>>> obj.bar = 'ni!' # value can also be set from the outside
>>> obj.bar         # no getter will be called
'ni!'

Using a different variable to cache data:

>>> class Foo(object):
...     @cachedproperty(varname='_some_var')
...     def bar(self):
...         return "result of intensive calculation"
>>> obj = Foo()
>>> obj.bar
'result of intensive calculation'
>>> obj._some_var   # cached data will be stored under custom name
'result of intensive calculation'