python使用pickle,json等序列化dict

import pickle, json, csv, os, shutil

class PersistentDict(dict):

    ''' Persistent dictionary with an API compatible with shelve and anydbm.

    The dict is kept in memory, so the dictionary operations run as fast as

    a regular dictionary.

    Write to disk is delayed until close or sync (similar to gdbm's fast mode).

    Input file format is automatically discovered.

    Output file format is selectable between pickle, json, and csv.

    All three serialization formats are backed by fast C implementations.

    '''

    def __init__(self, filename, flag='c', mode=None, format='pickle', *args, **kwds):

        self.flag = flag                    # r=readonly, c=create, or n=new

        self.mode = mode                    # None or an octal triple like 0644

        self.format = format                # 'csv', 'json', or 'pickle'

        self.filename = filename

        if flag != 'n' and os.access(filename, os.R_OK):

            fileobj = open(filename, 'rb' if format=='pickle' else 'r')

            with fileobj:

                self.load(fileobj)

        dict.__init__(self, *args, **kwds)

    def sync(self):

        'Write dict to disk'

        if self.flag == 'r':

            return

        filename = self.filename

        tempname = filename + '.tmp'

        fileobj = open(tempname, 'wb' if self.format=='pickle' else 'w')

        try:

            self.dump(fileobj)

        except Exception:

            os.remove(tempname)

            raise

        finally:

            fileobj.close()

        shutil.move(tempname, self.filename)    # atomic commit

        if self.mode is not None:

            os.chmod(self.filename, self.mode)

    def close(self):

        self.sync()

    def __enter__(self):

        return self

    def __exit__(self, *exc_info):

        self.close()

    def dump(self, fileobj):

        if self.format == 'csv':

            csv.writer(fileobj).writerows(self.items())

        elif self.format == 'json':

            json.dump(self, fileobj, separators=(',', ':'))

        elif self.format == 'pickle':

            pickle.dump(dict(self), fileobj, 2)

        else:

            raise NotImplementedError('Unknown format: ' + repr(self.format))

    def load(self, fileobj):

        # try formats from most restrictive to least restrictive

        for loader in (pickle.load, json.load, csv.reader):

            fileobj.seek(0)

            try:

                return self.update(loader(fileobj))

            except Exception:

                pass

        raise ValueError('File not in a supported format')

if __name__ == '__main__':

    import random

    # Make and use a persistent dictionary

    with PersistentDict('/tmp/demo.json', 'c', format='json') as d:

        print(d, 'start')

        d['abc'] = '123'

        d['rand'] = random.randrange(10000)

        print(d, 'updated')

    # Show what the file looks like on disk

    with open('/tmp/demo.json', 'rb') as f:

        print(f.read())
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python使用pickle,json等序列化dict

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