TypeError: cannot pickle '_thread.lock' object [Solved]

# TypeError: cannot pickle '_thread.lock' object [Solved]

The Python "TypeError: cannot pickle '_thread.lock' object" occurs when you try to pickle a _thread.lock object.

To solve the error, remove the _thread.lock object before pickling.

Here is an example of how the error occurs.

main.py

Copied!
import pickle
import threading

a_dict = {
    'website': 'bobbyhadz.com',
    'topic': 'Python',
    'lock_object': threading.Lock()
}

# ⛔️ TypeError: cannot pickle '_thread.lock' object
with open('example.pickle', 'wb') as file_handle:
    pickle.dump(a_dict, file_handle, protocol=pickle.HIGHEST_PROTOCOL)

typeerror cannot pickle thread lock object

The code for this article is available on GitHub

Notice that the dictionary contains a key that points to a lock object.

Pickling a lock object is not allowed and so the error is raised.

The threading.Lock class is used to create lock objects.

Once a thread has acquired a lock, subsequent attempts to acquire it block until it is released.

# Removing the `lock` object before pickling

One way to solve the error is to remove the lock object before pickling.

main.py

Copied!
import pickle
import threading

a_dict = {
    'website': 'bobbyhadz.com',
    'topic': 'Python',
    'lock_object': threading.Lock()
}

del a_dict['lock_object']

with open('example.pickle', 'wb') as file_handle:
    pickle.dump(a_dict, file_handle, protocol=pickle.HIGHEST_PROTOCOL)

removing the lock object before pickling

The code for this article is available on GitHub

The code sample uses the del statement to remove the lock_object key from the dictionary.

You might also have gotten the error when storing a lock object in a list.

main.py

Copied!
import pickle
import threading

a_list = ['bobby', 'hadz', 'com', threading.Lock()]

# ⛔️ TypeError: cannot pickle '_thread.lock' object
with open('example.pickle', 'wb') as file_handle:
    pickle.dump(a_list, file_handle, protocol=pickle.HIGHEST_PROTOCOL)

You can iterate over the list and remove all lock objects before pickling.

main.py

Copied!
import pickle
import threading

a_list = ['bobby', 'hadz', 'com', threading.Lock()]

for item in a_list.copy():
    if hasattr(item, 'release') and hasattr(item, 'locked'):
        a_list.remove(item)

with open('example.pickle', 'wb') as file_handle:
    pickle.dump(a_list, file_handle, protocol=pickle.HIGHEST_PROTOCOL)

The code for this article is available on GitHub

We used a for loop to iterate over a copy of the list.

Iterating over a copy is necessary because you aren't allowed to remove items from a list while iterating over it.

On each iteration, we check if the current item is a lock object.

If the condition is met, we remove the lock object from the list.

# Removing the lock object by using `getstate` in a class

You can also remove the lock object using a custom class.

main.py

Copied!
import pickle
import threading


class Pickler:
    def __init__(self):
        self.website = 'bobbyhadz.com'
        self.topic = 'Python'
        self.lock_object = threading.Lock()

    def __getstate__(self):
        state = self.__dict__.copy()

        print(state)

        # 👇️ don't pickle the lock_object key
        del state['lock_object']
        return state

obj1 = Pickler()

print(obj1)


with open('example.pickle', 'wb') as file_handle:
    pickle.dump(obj1, file_handle, protocol=pickle.HIGHEST_PROTOCOL)

    print('success')

delete lock object using getstate

The code for this article is available on GitHub

The object.__getstate__ method can be used to influence how instances are pickled.

The method is called and the returned object is pickled as the contents for the instance, instead of a default state.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

I wrote a book in which I share everything I know about how to become a better, more efficient programmer.

You can use the search field on my Home Page to filter through all of my articles.

TypeError: cannot pickle '_thread.lock' object [Solved]