Pickle problem

[Mario Ceresa]

Hello everybody:
I'd like to use the pickle module to save the state of an object so to
be able to restore it later. The problem is that it holds a list of
other objects, say numbers, and if I modify the list and restore the
object, the list itself is not reverted to the saved one, but stays
with one element deleted.
An example session is the following:

Data is A [1, 2, 3, 4]
saving a with pickle
Deleting an object: del a[3]
Now data is A [1, 2, 3]
Oops! That was an error: can you please recover to the last saved data?
A [1, 2, 3] #### I'd like to have here A[1,2,3,4]!!!!!!

Is it the intended behavior for pickle? if so, are there any way to
save the state of my object?

Code follows
-----------------------
class A(object):
objects = []
-----------------------
then I run the code:
---------------------------------------
import pickle
from core import A

a = A()

for i in [1,2,3,4]:
a.objects.append(i)

savedData = pickle.dumps(a)
print "Saved data is ",a
print "Deleting an object"
del a.objects[3]
print a
print "Oops! This was an error: can you please recover the last saved data?"

print pickle.loads(savedData)
--------------------------------------------

Thank you for any help!

Mario

[George Sakkis]

On Apr 18, 11:55*am, "Mario Ceresa" <[e-mail]:

Hello everybody:
I'd like to use the pickle module to save the state of an object so to
be able to restore it later. The problem is that it holds a list of
other objects, say numbers, and if I modify the list and restore the
object, the list itself is not reverted to the saved one, but stays
with one element deleted.
An example session is the following:

Data is *A [1, 2, 3, 4]
saving a with pickle
Deleting an object: del a[3]
Now data is A [1, 2, 3]
Oops! That was an error: can you please recover to the last saved data?
A [1, 2, 3] * * #### I'd like to have here A[1,2,3,4]!!!!!!

Is it the intended behavior for pickle? if so, are there any way to
save the state of my object?

Code follows
-----------------------
class A(object):
* * * * objects = []
-----------------------
then I run *the code:
---------------------------------------
import pickle
from core import A

a = A()

for i in [1,2,3,4]:
* * * * a.objects.append(i)

savedData = pickle.dumps(a)
print "Saved data is ",a
print "Deleting an object"
del a.objects[3]
print a
print "Oops! This was an error: can you please recover the last saved data?"

print pickle.loads(savedData)
--------------------------------------------

Thank you for any help!

Mario

The problem is that the way you define 'objects', it is an attribute
of the A *class*, not the instance you create. Change the A class to:

class A(object):
def __init__(self):
self.objects = []

and rerun it; it should now work as you intended.

HTH,
George

[Mario Ceresa]

Dear Jerry and George:
it works like a charm! I always thought that the first way was a
quicker alternative to defining the init method... shame on me!

>From now on I'll read the list every day repeating to myself:

"Premature optimization is the root of all evil", "Premature
optimization is the root of all evil", .... :)

Thanks a lot,

Mario
On Fri, Apr 18, 2008 at 8:00 PM, George Sakkis <ge***********@gmail.comwrote:

On Apr 18, 11:55 am, "Mario Ceresa" <[e-mail]:

Hello everybody:
I'd like to use the pickle module to save the state of an object so to
be able to restore it later. The problem is that it holds a list of
other objects, say numbers, and if I modify the list and restore the
object, the list itself is not reverted to the saved one, but stays
with one element deleted.

An example session is the following:
>
Data is A [1, 2, 3, 4]
saving a with pickle
Deleting an object: del a[3]
Now data is A [1, 2, 3]
Oops! That was an error: can you please recover to the last saved data?
A [1, 2, 3] #### I'd like to have here A[1,2,3,4]!!!!!!
>
Is it the intended behavior for pickle? if so, are there any way to
save the state of my object?
>
Code follows
-----------------------
class A(object):
objects = []
-----------------------
then I run the code:
---------------------------------------
import pickle
from core import A
>
a = A()
>
for i in [1,2,3,4]:
a.objects.append(i)
>
savedData = pickle.dumps(a)
print "Saved data is ",a
print "Deleting an object"
del a.objects[3]
print a
print "Oops! This was an error: can you please recover the last saved data?"
>
print pickle.loads(savedData)
--------------------------------------------
>
Thank you for any help!
>
Mario

The problem is that the way you define 'objects', it is an attribute
of the A *class*, not the instance you create. Change the A class to:
class A(object):
def __init__(self):
self.objects = []

and rerun it; it should now work as you intended.

HTH,
George
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