attribute save restore

[Carl K]

Is there a more elegant way of coding this:

x=o.p # save .p
o.p=0
o.m()
o.p=x # restore .p

seems very push/pop to me - like there should be a way that doesn't need a var
(x) or the save/set lines should be done in one command.

(personally I think .m would better be implemented by passing in a parameter,
but that isn't my choice.)

Carl K

 

[Steven Bethard]

Is there a more elegant way of coding this:

x=o.p # save .p
o.p=0
o.m()
o.p=x # restore .p

seems very push/pop to me - like there should be a way that doesn't need
a var (x) or the save/set lines should be done in one command.

With the appropriate context manger, you could write this as::

with setting(o, 'p', 2):
o.m()

Here's the code::
... def setting(obj, name, value):
... old_value = getattr(obj, name)
... setattr(obj, name, value)
... try:
... yield obj
... finally:
... setattr(obj, name, old_value)
... ... def __init__(self, x):
... self.x = x
... def m(self):
... print self.x
... ... c.m()
...
2 1

Of course, that just wraps up the same push/pop behavior you're doing
into a context manager.

(personally I think .m would better be implemented by passing in a
parameter, but that isn't my choice.)

Yep, that's the right answer. You should complain to whoever created
this API.

STeVe

 

[Carsten Haese]

Is there a more elegant way of coding this:

x=o.p # save .p
o.p=0
o.m()
o.p=x # restore .p

In Python 2.5, you could leverage the new "with" statement with a
properly crafted context manager along these lines:

"""
from __future__ import with_statement

class TempAttrSetter(object):
def __init__(self, obj, **attrs):
self.obj = obj
self.attrs = attrs

def __enter__(self):
self.saved_attrs = {}
for attr, newval in self.attrs.iteritems():
self.saved_attrs[attr] = getattr(self.obj, attr)
setattr(self.obj, attr, newval)

def __exit__(self, *args):
for attr in self.saved_attrs.keys():
setattr(self.obj, attr, self.saved_attrs[attr])

class Bag(object): pass
b = Bag()
b.x = 1

print b.x # prints 1
with TempAttrSetter(b, x=3):
print b.x # prints 3
print b.x # prints 1
"""

-Carsten

 

[Carl K]

With the appropriate context manger, you could write this as::

with setting(o, 'p', 2):
o.m()

Here's the code::

... def setting(obj, name, value):
... old_value = getattr(obj, name)
... setattr(obj, name, value)
... try:
... yield obj
... finally:
... setattr(obj, name, old_value)
...
... def __init__(self, x):
... self.x = x
... def m(self):
... print self.x
...
... c.m()
...
2
1

Of course, that just wraps up the same push/pop behavior you're doing
into a context manager.

Thanks.

As I was eating lunch I came up with:

x,o.p = o.p,0

Which I am pretty sure is just bad
I need to cut back on the hot sauce.

Yep, that's the right answer. You should complain to whoever created
this API.

Will do. Something is buggy anyway, so as long as I am commenting...

Carl K

 

[Bruno Desthuilliers]

Carl K a écrit :

Is there a more elegant way of coding this:

x=o.p # save .p
o.p=0
o.m()
o.p=x # restore .p

seems very push/pop to me - like there should be a way that doesn't need
a var (x) or the save/set lines should be done in one command.

(personally I think .m would better be implemented by passing in a
parameter, but that isn't my choice.)

I was about to comment on this. It looks like o.m is wanting to take an
optional arg defaulting to o.p, and you should probably propose a patch
to the author.

My 2 cents