How can I correctly save and load Python objects using pickle.dump?

General Discussions
1

I’m trying to save and load objects with the pickle module. For example:

class Fruits: pass
banana = Fruits()
banana.color = 'yellow'
banana.value = 30

import pickle
filehandler = open("Fruits.obj", "wb")
pickle.dump(banana, filehandler)
filehandler.close()

When I try to load it in a new session:

file = open("Fruits.obj", "rb")
object_file = pickle.load(file)

I get an EOFError. I also previously tried opening the file in text mode (‘r’) and got a ValueError. How can I correctly save and load my object using pickle.dump without errors?

2

I’ve faced this issue before :sweat_smile:. The main thing with pickle is that you must always open files in binary mode:

“wb” when saving

“rb” when loading

Here’s a clean example using your Fruits class:

import pickle

class Fruits:
    pass

# Saving the object
banana = Fruits()
banana.color = 'yellow'
banana.value = 30

with open("Fruits.obj", "wb") as f:
    pickle.dump(banana, f)

# Loading the object
with open("Fruits.obj", "rb") as f:
    banana_loaded = pickle.load(f)

print(banana_loaded.color)  # Output: yellow

I always prefer with statements, they automatically close the file, which prevents many EOFErrors or file corruption issues.

3

From my experience, EOFError usually happens if:

The file is opened in text mode (“w” or “r”). Always use “wb”/“rb”.

The file was not properly closed after writing. Using with fixes this.

You try to load an empty file or a file that wasn’t pickled.

I usually check the file size (os.path.getsize("Fruits.obj")) before loading, just to make sure it’s not zero bytes.

4

Sometimes I like to save multiple objects in the same file.

Here’s how I handle it:

apple = Fruits()
apple.color = 'red'
apple.value = 20

# Save multiple objects
with open("Fruits.obj", "wb") as f:
    pickle.dump(banana, f)
    pickle.dump(apple, f)

# Load multiple objects
with open("Fruits.obj", "rb") as f:
    banana_loaded = pickle.load(f)
    apple_loaded = pickle.load(f)

print(banana_loaded.color, apple_loaded.color)  # Output: yellow red

Note: You cannot append to a pickle file in the usual sense; you need to handle multiple objects like this.

I often use pickle.load in a loop with try/except EOFError when reading an unknown number of objects.