Python serialization – Why pickle?

Pickling is a way to convert a python object (list, dict, etc.) into a character stream. The idea is that this character stream contains all the information necessary to reconstruct the object in another python script. As for where the pickled information is stored, usually one would do: with open(‘filename’, ‘wb’) as f: var = … Read more

ValueError: unsupported pickle protocol: 3, python2 pickle can not load the file dumped by python 3 pickle?

You should write the pickled data with a lower protocol number in Python 3. Python 3 introduced a new protocol with the number 3 (and uses it as default), so switch back to a value of 2 which can be read by Python 2. Check the protocolparameter in pickle.dump. Your resulting code will look like … Read more

Cannot load pickled object

You need to either read the file first (as binary bytes) and use pickle.loads(), or pass an open file object to the pickle.load() command. The latter is preferable: with open(‘out/cache/’ +hashed_url, ‘rb’) as pickle_file: content = pickle.load(pickle_file) Neither method supports loading a pickle from a filename.

How to unpack pkl file?

Generally Your pkl file is, in fact, a serialized pickle file, which means it has been dumped using Python’s pickle module. To un-pickle the data you can: import pickle with open(‘serialized.pkl’, ‘rb’) as f: data = pickle.load(f) For the MNIST data set Note gzip is only needed if the file is compressed: import gzip import … Read more

Preferred (or most common) file extension for a Python pickle

Python 2 From the Python 2 documentation, while serializing (i.e. writing to a pickle file), use: output = open(‘data.pkl’, ‘wb’) I would choose .pkl as the extension when using Python 2. Python 3 The example in the Python 3 documentation now uses .pickle as the file extension for serialization: with open(‘data.pickle’, ‘wb’) as f: pickle.dump(…) … Read more

Is there an easy way to pickle a python function (or otherwise serialize its code)?

You could serialise the function bytecode and then reconstruct it on the caller. The marshal module can be used to serialise code objects, which can then be reassembled into a function. ie: import marshal def foo(x): return x*x code_string = marshal.dumps(foo.__code__) Then in the remote process (after transferring code_string): import marshal, types code = marshal.loads(code_string) … Read more

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