python使用pickle,json等序列化dict详解编程语言

PersistentDict从dict继承，实现了持久化。初始化时自动加载文件到内存，关闭时将dict内容序列化到文件，支持csv，json，pickle格式。

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 gdbms 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()) 

原创文章，作者：Maggie-Hunter，如若转载，请注明出处：https://blog.ytso.com/8153.html