zoukankan      html  css  js  c++  java
  • 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())
  • 相关阅读:
    webStorage和cookie相比存在的优势
    session、localStorage和cookie之间的区别
    了解常见的状态码
    什么情况下会碰到跨域问题?有哪些方法可以解决
    什么是跨域?跨域请求资源的方式有哪些?
    垃圾回收机制
    400,500错误
    Junit添加完maven依赖无法使用@Test
    Maven资源过滤问题处理
    javascript的一些注意点
  • 原文地址:https://www.cnblogs.com/DjangoBlog/p/6679603.html
Copyright © 2011-2022 走看看