Ways to Solve Can't Pickle local object Error

We all have seen an error occurred named Attribute error in python. This error occurs while we try to call an attribute of an object, whose type does not support that method. Now we are going to see one of the attribute errors namely can’t pickle local objects. Here we are will how this error occurs and how to solve this error. Let us start.

Pickling is the process of converting an object into a byte stream to store it in either a file or database. These pickled objects are useful to recreate the python original objects. Simply it is converting an object into a character stream. It is similar to packages. We can reconstruct all the objects in another python script.

Contents

Disadvantages in Python pickling

Different versions of python files will not work properly while unpickling. This the major disadvantages of python. Pickling is not allowed in different languages. So pickling and unpickling are only possible in the same versions of the python file.

Can’t Pickle local objects

Many of the time we will face an error as an Attribute error. It shows like can’t pickle local objects. Let us see why this error occurs and how to solve that.

Example 1: Attribute Error – can’t pickle local objects

import pickle
def function():
    class result: pass
    return result
Localresult=function()
a=Localresult()
with open("sample.pickle","wb") as f:
    pickle.dump(a,f,pickle.HIGHEST_PROTOCOL)
print("Program Finished")

We have imported pickle. Create a function and create a class. Creating a binary file named sample, in a write mode. We are trying to pickle local objects but it shows an attribute error. Let us see what happens now.

Output

Traceback (most recent call last):
  File "C:\Users\AppData\Local\Programs\Python\Python39\78.py", line 83, in <module>
    pickle.dump(a,f,pickle.HIGHEST_PROTOCOL)
AttributeError: Can't pickle local object 'function.<locals>.result'

Example 1: Solving Attribute error

import pickle
def function():
    global result
    class result: pass
    return result
Localresult=function()
a=Localresult()
with open("sample.pickle","wb") as f:
    pickle.dump(a,f,pickle.HIGHEST_PROTOCOL)
print("Program Finished")

To solve this type of error we have to declare that variable as global variables. We can’t pickle local objects so that we are declaring that variable result as global. Here we have given only one print statement. If it is declared then we can say that the program has run successfully.

Output

Program Finished

Example 2: Attribute error while multiprocessing – can’t pickle local objects

import multiprocessing
def function():
    a="string"
    def fun1():
        print(a)
    var1=multiprocessing.Process(target=fun1,args=(a))
    if __name__ == "__main__":
        var1.start()
        var1.join()
function()
print("Program finished")

In this program, we are going to see how to rectify the attribute error while multiprocessing. Import multiprocessing. Create a function. We are trying to process the function by declaring it as a local object. But it shows an error. So that we are trying to pickle an object as a global object.

Example 2: Solving Attribute Error

import multiprocessing
def function():
    global fun1
    a="string"
    def fun1():
        print(a)
    var1=multiprocessing.Process(target=fun1,args=(a))
    if __name__ == "__main__":
        var1.start()
        var1.join()
function()
print("Program finished")

Now we are declaring it as global so that we can pickle objects easily. Now the program will run properly without any errors.

Output

Program finished

Can’t pickle local object while using lambda functions

import pickle
var=pickle.dumps(lambda x,y:x+y)
var1=pickle.loads(var1)

We can’t pickle objects while we are using lambda functions. If we try to pickle it shows an error like can’t pickle lambda functions objects.

Output

Traceback (most recent call last):
  File "C:/Users/AppData/Local/Programs/Python/Python39/pu.py", line 10, in <module>
    var=pickle.dumps(lambda x,y:x+y)
_pickle.PicklingError: Can't pickle <function <lambda> at 0x000001555D4FAF70>: attribute lookup <lambda> on __main__ failed

Can’t pickle local object ‘_createenviron.locals.encode key’ ?

There are many situations where you create helper functions to help your main tasks. But while dealing with chrome drivers, you may face can’t pickle errors depending on your function scope.

When using the flask application in production mode, there are different instances of workers handling the traffic. In such cases, the chrome driver will not be saved from the custom function if it’s called by a different worker.

So, make sure you create the chrome driver inside your helper function.

1. Is it possible to pickle with different versions of python files?

No, pickling is only possible with the same versions of python files.

2. Does pickle save the objects in human-readable format?

No, it doesn’t save the objects in the human-readable format.

3. Can we use Joblib instead of Pickle?

Yes, We can use joblib instead of pickle. It is also more efficient on big data.

Conclusion

Here we have seen an attribute error occurs in python. And we saw how to overcome it. We hope this article is very much helpful for you. Learn it. In case of any queries let us know in the comment section. We will help you. Try to implement the programs on your own.