On 20 июл, 15:00, Jean-Michel Pichavant <jeanmic...@sequans.com> wrote: > dmitrey wrote: > > hi all, > > I have a class (FuncDesigner oofun) that has no attribute "size", but > > it is overloaded in __getattr__, so if someone invokes > > "myObject.size", it is generated (as another oofun) and connected to > > myObject as attribute. > > > So, when I invoke in other code part "hasattr(myObject, 'size')", > > instead o returning True/False it goes to __getattr__ and starts > > constructor for another one oofun, that wasn't intended behaviour. > > Thus "hasattr(myObject, 'size')" always returns True. It prevents me > > of some bonuses and new features to be done in FuncDesigner. > > >>>> 'size' in dir(b) > > > False > > >>>> hasattr(b,'size') > > > True > > >>>> 'size' in dir(b) > > > True > > > Could you fix it? > > Quite simple, when calling b.size, return the computed value but do not > set it as attribute, the value will be computed on each b.size call, and > hasattr w. If you don't want to compute it each time, cause there no > reason for it to change, use a private dummy attribute to record the > value instead of size (__size for instance) and return the value of > __size when getting the value of size. > > class Foo(object): > def __init__(self): > self.__size = None > > def __getattr__(self, name): > if name == "size": > if self.__size is None: > self.__size = 5 # compute the value > return self.__size > raise AttributeError(name) > > b = Foo() > print 'size' in dir(b) > print hasattr(b, 'size') > print 'size' in dir(b) > > False > True > False > > JM
This doesn't stack with the following issue: sometimes user can write in code "myObject.size = (some integer value)" and then it will be involved in future calculations as ordinary fixed value; if user doesn't supply it, but myObject.size is involved in calculations, then the oofun is created to behave like similar numpy.array attribute. -- http://mail.python.org/mailman/listinfo/python-list
