dmitrey wrote:
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.
Here are some solutions in my humble order of preference:
1/ ask the user to always fill the size field
2/ ask the user to never fill the size filed (you can override
__setattr__ to make sure...)
3/ override __setattr__ to set __size instead of size
JM
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