changing __getattr__ dynamically

[Dan Bentley]

class foo(object):
def __getattr__(sel f, 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

[Peter Otten]

Dan Bentley wrote:

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.

class foo(object): .... def __getattr__(sel f, name):
.... return 42
.... def e(self, name): .... return 2.7
.... bar = foo()
print bar.baz 42 bar.__class__._ _getattr__ = e
print bar.baz

2.7

Peter

[Peter Otten]

Dan Bentley wrote:

class foo(object):
def __getattr__(sel f, 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:

class foo(object): .... def e(self): return "in class"
.... def ee(self): .... return "in instance"
.... bar = foo()
bar.e() 'in class' bar.e = ee
bar.e() 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
import new
bar.e = new.instancemet hod(ee, bar)
bar.e() 'in instance' foo().e()

'in class'

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

Peter