How can I use pickle to save a dict?

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说谎
说谎 2020-11-22 06:45

I have looked through the information that the Python docs give, but I\'m still a little confused. Could somebody post sample code that would write a new file then use pickl

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  • 2020-11-22 07:29
    # Save a dictionary into a pickle file.
    import pickle
    
    favorite_color = {"lion": "yellow", "kitty": "red"}  # create a dictionary
    pickle.dump(favorite_color, open("save.p", "wb"))  # save it into a file named save.p
    
    # -------------------------------------------------------------
    # Load the dictionary back from the pickle file.
    import pickle
    
    favorite_color = pickle.load(open("save.p", "rb"))
    # favorite_color is now {"lion": "yellow", "kitty": "red"}
    
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  • 2020-11-22 07:30

    I've found pickling confusing (possibly because I'm thick). I found that this works, though:

    myDictionaryString=str(myDictionary)
    

    Which you can then write to a text file. I gave up trying to use pickle as I was getting errors telling me to write integers to a .dat file. I apologise for not using pickle.

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  • 2020-11-22 07:35

    If you just want to store the dict in a single file, use pickle like that

    import pickle
    
    a = {'hello': 'world'}
    
    with open('filename.pickle', 'wb') as handle:
        pickle.dump(a, handle)
    
    with open('filename.pickle', 'rb') as handle:
        b = pickle.load(handle)
    

    If you want to save and restore multiple dictionaries in multiple files for caching and store more complex data, use anycache. It does all the other stuff you need around pickle

    from anycache import anycache
    
    @anycache(cachedir='path/to/files')
    def myfunc(hello):
        return {'hello', hello}
    

    Anycache stores the different myfunc results depending on the arguments to different files in cachedir and reloads them.

    See the documentation for any further details.

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  • 2020-11-22 07:36
    import pickle
    
    dictobj = {'Jack' : 123, 'John' : 456}
    
    filename = "/foldername/filestore"
    
    fileobj = open(filename, 'wb')
    
    pickle.dump(dictobj, fileobj)
    
    fileobj.close()
    
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  • 2020-11-22 07:38

    In general, pickling a dict will fail unless you have only simple objects in it, like strings and integers.

    Python 2.7.9 (default, Dec 11 2014, 01:21:43) 
    [GCC 4.2.1 Compatible Apple Clang 4.1 ((tags/Apple/clang-421.11.66))] on darwin
    Type "help", "copyright", "credits" or "license" for more information.
    >>> from numpy import *
    >>> type(globals())     
    <type 'dict'>
    >>> import pickle
    >>> pik = pickle.dumps(globals())
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 1374, in dumps
        Pickler(file, protocol).dump(obj)
      File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 224, in dump
        self.save(obj)
      File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
        f(self, obj) # Call unbound method with explicit self
      File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 649, in save_dict
        self._batch_setitems(obj.iteritems())
      File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 663, in _batch_setitems
        save(v)
      File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 306, in save
        rv = reduce(self.proto)
      File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/copy_reg.py", line 70, in _reduce_ex
        raise TypeError, "can't pickle %s objects" % base.__name__
    TypeError: can't pickle module objects
    >>> 
    

    Even a really simple dict will often fail. It just depends on the contents.

    >>> d = {'x': lambda x:x}
    >>> pik = pickle.dumps(d)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 1374, in dumps
        Pickler(file, protocol).dump(obj)
      File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 224, in dump
        self.save(obj)
      File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
        f(self, obj) # Call unbound method with explicit self
      File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 649, in save_dict
        self._batch_setitems(obj.iteritems())
      File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 663, in _batch_setitems
        save(v)
      File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
        f(self, obj) # Call unbound method with explicit self
      File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 748, in save_global
        (obj, module, name))
    pickle.PicklingError: Can't pickle <function <lambda> at 0x102178668>: it's not found as __main__.<lambda>
    

    However, if you use a better serializer like dill or cloudpickle, then most dictionaries can be pickled:

    >>> import dill
    >>> pik = dill.dumps(d)
    

    Or if you want to save your dict to a file...

    >>> with open('save.pik', 'w') as f:
    ...   dill.dump(globals(), f)
    ... 
    

    The latter example is identical to any of the other good answers posted here (which aside from neglecting the picklability of the contents of the dict are good).

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  • 2020-11-22 07:40

    Simple way to dump a Python data (e.g. dictionary) to a pickle file.

    import pickle
    
    your_dictionary = {}
    
    pickle.dump(your_dictionary, open('pickle_file_name.p', 'wb'))
    
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