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pythonpython-3.xooppickledill

How can I change the definition of class methods after pickling

I am writing a class that does some data processing. I initiated the class and did some processing then pickled the results. the problem is that I added new methods to the class and loaded the pickled objects but I couldn't apply the new methods to the unpickled ones.

For example, This is my class

class Play(ABC):
  def __init__(self, data):
    self.data = data
    
  @abstractmethod
  def method(self):
    pass

class M(Play):

  def __init__(self, data):
    super().__init__(data)

  def method(self):
    self.corr = np.corrcoef(self.data)

I did some processing

mat = np.random.rand(102, 641)
s = M(mat)
s.method()

and pickled them using dill

def save_object(obj, filename):
    with open(filename, 'wb') as output:  
        dill.dump(obj, output, dill.HIGHEST_PROTOCOL)
save_object(s, 'file.pkl')

then, I added new methods to the class and unpickled the file to apply those methods but I couldn't

class Play(ABC):
  def __init__(self, data):
    self.data = data
    
  @abstractmethod
  def method(self):
    pass

class M(Play):

  def __init__(self, data):
    super().__init__(data)

  def method(self):
    self.corr = np.corrcoef(self.data)
  
  def new(self):
    # pass
    self.q = self.corr.shape
def load_object(filename):
  with open(filename, 'rb') as input:
    obj = dill.load(input)
    return obj

obj = load_object('file.pkl')
obj.new()

and I get this result

AttributeError: 'M' object has no attribute 'new'

How can I fix that?

Solution

  • An alternative for you is to use joblib library. I will also encourage you to check the documentation for joblib shared in the References section below.

    joblib.dump(obj, "filename.joblib")    ## Saving object to a file
obj = joblib.load("filename.joblib")   ## Loading object from a file

    Save and Load your object: 1st time

    class Foo(object):
    x = 1

    def bar(self, y):
        return y + self.x

f1 = Foo()

def checkFoo(foo: Foo):
    print(f'version: {foo.version}')

## save your object
>>> version = '0.0.1'
>>> f1.version = version
>>> checkFoo(f1)
'0.0.1'
>>> joblib.dump(f1, f'object_store_v{version}.joblib')
['object_store_v0.0.1.joblib']

## load saved object (latest version)
>>> version = '0.0.1'
>>> f2 = joblib.load(f'object_store_v{version}.joblib')
>>> checkFoo(f2)
'0.0.1'

    Save and Load your object: 2nd time (after modification)

    ## Modify object and save new version
>>> version = '0.0.2'
>>> f2.version = version
>>> checkFoo(f2)
'0.0.2'
>>> joblib.dump(f2, f'object_store_v{version}.joblib')
['object_store_v0.0.2.joblib']

## load saved object (latest version)
>>> version = '0.0.2'
>>> f3 = joblib.load(f'object_store_v{version}.joblib')
>>> checkFoo(f3)
'0.0.2'

    References