python常用庫有哪些，python的shelve庫

1、shelve模塊是一個簡單的key，value將內存數據通過文件持久化的模塊
2、shelve模塊可以持久化任何pickle可支持的python數據格式
3、shelve就是pickle模塊的一個封裝
4、shelve模塊是可以多次dump和load

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https://docs.python.org/3.6/library/shelve.html

1、該模塊底層使用dbm模塊做存儲，具體使用的是dbm.gnu還是dbm.ndbm，由運行時看哪個裝了就用哪個，否則用dbm.dumb

2、不支持并發讀寫，但是支持并發讀

#!/usr/bin/env python
#coding=utf-8
import shelve
import threadingclass A(object):
  """一個用于測試的類 其中只打印出hello和bye
  """def __init__(self, name):self.name = nameself.__actions = ['hello', 'bye']
def _hello(self):print ('hello, %s' % self.name)
def _bye(self):print ('bye, %s' % self.name)
def act(self):for a in self.__actions:if callable(getattr(self, '_'+a)):getattr(self, '_'+a)()FILENAME = 'shelve_test'
KEY = 'myobj'
DATA = A('qx')def test1():
  """基本用法
  """with shelve.open(FILENAME) as d:d[KEY] = DATAdata = d[KEY]print ('type(data)=%s' % type(data))del d[KEY]try:data = d[KEY]except KeyError:print ('key=%s not found' % KEY)d[KEY] = DATAdef test2():
  """當沒有使用write_back=True時 shelve無法檢測到可變對象的更新
  """with shelve.open(FILENAME) as d:d['xx'] = [0, 1, 2]print ("d['xx']=", d['xx'])  # [0, 1, 2]d['xx'].append(3)print ("d['xx']=", d['xx'])  # [0, 1, 2]def test3():
  """繼續test2 只能通過重新賦值來更新d['xx']
  """with shelve.open(FILENAME) as d:d['xx'] = [0, 1, 2]print ("d['xx']=", d['xx'])  # [0, 1, 2]data = d['xx']data.append(3)d['xx'] = dataprint ("d['xx']=", d['xx'])  # [0, 1, 2, 3]def test4(flag=None):
  """不支持并發讀寫 這是由Unix文件系統的文件鎖保證的 但是支持多線程并發讀
  """if flag is None: flag = 'c'def _test():d = shelve.open(FILENAME, flag=flag)try:data = d[KEY]except Exception as exc:print ('exception:%s' % exc)else:data.act()print (d['xx'])finally:d.close()
t1 = threading.Thread(target=_test)t2 = threading.Thread(target=_test)t1.start();t2.start()t1.join();t2.join()def split(seq):
  """打印分隔線
  """print ('====test %d====' % seq)if __name__ == '__main__':split(1);test1()  # key=myobj not foundsplit(2);test2()split(3);test3()split(4);test4('r')  # 如果調用test4() 會報異常 Resource temporarily unavailable

python常用庫有哪些。?