How to read pickle file?

Question

I created some data and stored it several times like this:

with open('filename', 'a') as f:
        pickle.dump(data, f)

Every time the size of file increased, but when I open file

with open('filename', 'rb') as f:
    x = pickle.load(f)

I can see only data from the last time. How can I correctly read file?

Answer 1

Pickle serializes a single object at a time, and reads back a single object - the pickled data is recorded in sequence on the file.

If you simply do pickle.load you should be reading the first object serialized into the file (not the last one as you've written).

After unserializing the first object, the file-pointer is at the beggining of the next object - if you simply call pickle.load again, it will read that next object - do that until the end of the file.

objects = []
with (open("myfile", "rb")) as openfile:
    while True:
        try:
            objects.append(pickle.load(openfile))
        except EOFError:
            break

Answer 2

There is a read_pickle function as part of pandas 0.22+

import pandas as pd

obj = pd.read_pickle(r'filepath')

Answer 3

The following is an example of how you might write and read a pickle file. Note that if you keep appending pickle data to the file, you will need to continue reading from the file until you find what you want or an exception is generated by reaching the end of the file. That is what the last function does.

import os
import pickle


PICKLE_FILE = 'pickle.dat'


def main():
    # append data to the pickle file
    add_to_pickle(PICKLE_FILE, 123)
    add_to_pickle(PICKLE_FILE, 'Hello')
    add_to_pickle(PICKLE_FILE, None)
    add_to_pickle(PICKLE_FILE, b'World')
    add_to_pickle(PICKLE_FILE, 456.789)
    # load & show all stored objects
    for item in read_from_pickle(PICKLE_FILE):
        print(repr(item))
    os.remove(PICKLE_FILE)


def add_to_pickle(path, item):
    with open(path, 'ab') as file:
        pickle.dump(item, file, pickle.HIGHEST_PROTOCOL)


def read_from_pickle(path):
    with open(path, 'rb') as file:
        try:
            while True:
                yield pickle.load(file)
        except EOFError:
            pass


if __name__ == '__main__':
    main()

Answer 4

I developed a software tool that opens (most) Pickle files directly in your browser (nothing is transferred so it's 100% private):

https://pickleviewer.com/ (formerly)

Now it's hosted here: https://fire-6dcaa-273213.web.app/

Edit: Available here if you want to host it somewhere: https://github.com/ch-hristov/Pickle-viewer

Feel free to host this somewhere.