Can I pickle "self" of a python class?

Question

I intend to save all my class variables at the current stage and load them later for replicating the same work. I tried to pickle all the object instance of the class but I guess since I created another sub object in the target object, it cannot pickle. My another solution is to pickle objects "self" to reload all the class wide variables for later use. Is it viable through pickle or what do you suggest?

For instance I have

class A:
...

class B:
...
def __init__():
    self.A_ins = A
    self.var1 = ...
    self.var2 = ...

b = B()
f = open(file_name,'wb')
pickle.dump(b,f)

This is the error I got, if I try to pickle directly

TypeError: can't pickle instancemethod objects

In this example I try to save Class B object and reload it later. If it is not possible because of sub object A_ins, I propose to pickle self of class B object and reload it.

how exactly have you tried to use `pickle` in the above code plz? what is the error message / unexpected behaviour you got? — Aprillion, Dec 14 '14 at 13:24
So... what was the solution? Please mark the answer that gave you the solution if any. And if not just comment why not. — J Agustin Barrachina, Feb 18 '20 at 16:05

score 1 · Answer 1 · answered Dec 14 '14 at 15:55

1

It looks as though you're setting self.A_ins to the class A, not to an instance of class A. That could be your problem -- you're trying to pickle the __init__() method of A.

Try changing self.A_ins = A to self.A_ins = A().

answered Dec 14 '14 at 15:55

kronosapiens

1,333
1
10
19

score 0 · Answer 2 · answered Dec 15 '14 at 13:26

You can't pickle that with pickle, however if you use dill, this should not be a problem. dill should be able to pickle B regardless if have an instance of A or the class object A (as you have above).

Python 3.3.5 (default, Mar 10 2014, 21:37:38) 
[GCC 4.2.1 Compatible Apple Clang 4.1 ((tags/Apple/clang-421.11.66))] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> class A:
...   pass
... 
>>> class B:
...   def __init__(self):
...     self.A_ins = A 
...     self.var1 = 1
...     self.var2 = 2
... 
>>> b = B()
>>>   
>>> import dill
>>> dill.dumps(b)
b'\x80\x03cdill.dill\n_create_type\nq\x00(cdill.dill\n_load_type\nq\x01X\x04\x00\x00\x00typeq\x02\x85q\x03Rq\x04X\x01\x00\x00\x00Bq\x05h\x01X\x06\x00\x00\x00objectq\x06\x85q\x07Rq\x08\x85q\t}q\n(X\r\x00\x00\x00__slotnames__q\x0b]q\x0cX\n\x00\x00\x00__module__q\rX\x08\x00\x00\x00__main__q\x0eX\x08\x00\x00\x00__init__q\x0fcdill.dill\n_create_function\nq\x10(cdill.dill\n_unmarshal\nq\x11C\xb0c\x01\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x02\x00\x00\x00C\x00\x00\x00s\x1f\x00\x00\x00t\x00\x00|\x00\x00_\x01\x00d\x01\x00|\x00\x00_\x02\x00d\x02\x00|\x00\x00_\x03\x00d\x00\x00S(\x03\x00\x00\x00Ni\x01\x00\x00\x00i\x02\x00\x00\x00(\x04\x00\x00\x00u\x01\x00\x00\x00Au\x05\x00\x00\x00A_insu\x04\x00\x00\x00var1u\x04\x00\x00\x00var2(\x01\x00\x00\x00u\x04\x00\x00\x00self(\x00\x00\x00\x00(\x00\x00\x00\x00u\x07\x00\x00\x00<stdin>u\x08\x00\x00\x00__init__\x02\x00\x00\x00s\x06\x00\x00\x00\x00\x01\t\x01\t\x01q\x12\x85q\x13Rq\x14c__builtin__\n__main__\nh\x0fNN}q\x15tq\x16Rq\x17X\x07\x00\x00\x00__doc__q\x18Nutq\x19Rq\x1a)\x81q\x1b}q\x1c(X\x05\x00\x00\x00A_insq\x1dh\x00(h\x04X\x01\x00\x00\x00Aq\x1eh\x08\x85q\x1f}q (h\x18Nh\rh\x0eutq!Rq"X\x04\x00\x00\x00var2q#K\x02X\x04\x00\x00\x00var1q$K\x01ub.'
>>> 
>>> _b = dill.loads(dill.dumps(b))
>>> _b.A_ins 
<class '__main__.A'>
>>>

The above will pickle your class regardless of you using python 2 or python 3. `dill` can pickle both old and new style classes, as well. — Mike McKerns, Dec 15 '14 at 13:40
Also see: http://stackoverflow.com/questions/2709800/how-to-pickle-yourself/25128214#25128214 — Mike McKerns, Dec 15 '14 at 13:42

jarondl · Answer 3 · 2014-12-15T13:47:49.993

0

If you are on Python2, you have classic classes, which are unpickelable. Try to inherit from object, i.e. replace class A: with class A(object):.

If you are on Python3 I guess you have a different problem, since newstyle is the default. https://docs.python.org/2/reference/datamodel.html#newstyle

EDIT:

Do not assume OP uses Python2

edited Dec 15 '14 at 13:47

answered Dec 15 '14 at 13:33

jarondl

1,593
4
18
27

1

Where does the OP say it's Python2? – Mike McKerns Dec 15 '14 at 13:39
2

I must have imagined it – jarondl Dec 15 '14 at 13:44

Can I pickle "self" of a python class?

3 Answers3

EDIT: