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  • 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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  • 原文地址:https://www.cnblogs.com/DjangoBlog/p/6679603.html
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