changing __getattr__ dynamically

[Dan Bentley]

class foo(object):
def __getattr__(self, name):
return 42

def e(self, name):
return 2.7

bar = foo()
print bar.baz
bar.__getattr__ = e
print bar.baz

I'd expect this to print:
42
2.7

But instead it prints:
42
42

Is there a way to change the actual __getattr__ used at runtime?

-D"python 2.3.3 on Mac OS X 10.3.4"an

 

[Satchidanand Haridas]

class foo(object):
def __getattr__(self, name):
return 42

def e(self, name):
return 2.7

bar = foo()
print bar.baz
bar.__getattr__ = e
print bar.baz

I'd expect this to print:
42
2.7

But instead it prints:
42
42

Is there a way to change the actual __getattr__ used at runtime?

-D"python 2.3.3 on Mac OS X 10.3.4"an

The following code will do so:

<code>

class foo(object):

def __getattr__(self, name):
if 'attrFunc' in self.__dict__:
return self.__dict__['attrFunc'](name)
else:
return 42

def __setattr__(self,name,value):
self.__dict__[name] = value

def e(self,name):
return 27

bar = foo()
print bar.baz
bar.attrFunc = bar.e
print bar.baz

</code>

Regards,
Satchit

----
Satchidanand Haridas (sharidas at zeomega dot com)

ZeOmega (www.zeomega.com)
Open Minds' Open Solutions

#20,Rajalakshmi Plaza,
South End Road,
Basavanagudi,
Bangalore-560 004, India

 

[Peter Otten]

Is there a way to change the actual __getattr__ used at runtime?

Special methods are always looked up in the class, any changes must
therefore be made in the class and will affect all instances.
.... def __getattr__(self, name):
.... return 42
........ return 2.7
....2.7

Peter

 

[Peter Otten]

class foo(object):
def __getattr__(self, name):
return 42

def e(self, name):
return 2.7

bar = foo()
print bar.baz
bar.__getattr__ = e
print bar.baz

I'd expect this to print:
42
2.7

But instead it prints:
42
42

Is there a way to change the actual __getattr__ used at runtime?

One more note - the above wouldn't work for "normal" methods, too:
.... def e(self): return "in class"
........ return "in instance"
....Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: ee() takes exactly 1 argument (0 given)

I.e. if you assign a function to an instance attribute, self will not be
passed implicitely. Instead
'in class'

will achieve the desired specialization for the modified foo instance while
preserving the standard behaviour.

Peter