import shelve
d = shelve.open(filename) # open -- file may get suffix added by low-level
# library
d[key] = data # store data at key (overwrites old data if
# using an existing key)
data = d[key] # retrieve a COPY of data at key (raise KeyError if no
# such key)
del d[key] # delete data stored at key (raises KeyError
# if no such key)
flag = key in d # true if the key exists
klist = list(d.keys()) # a list of all existing keys (slow!)
# as d was opened WITHOUT writeback=True, beware:
d['xx'] = [0, 1, 2] # this works as expected, but...
d['xx'].append(3) # *this doesn't!* -- d['xx'] is STILL [0, 1, 2]!
# having opened d without writeback=True, you need to code carefully:
temp = d['xx'] # extracts the copy
temp.append(5) # mutates the copy
d['xx'] = temp # stores the copy right back, to persist it
# or, d=shelve.open(filename,writeback=True) would let you just code
# d['xx'].append(5) and have it work as expected, BUT it would also
# consume more memory and make the d.close() operation slower.
d.close() # close it
要从二进制文件中删除pickled对象,必须重写整个文件。
pickle
模块不处理流的任意部分的修改,因此没有内置的方法来做您想要的事情。可能二进制文件最简单的替代方法是使用^{} 模块。
这个模块提供了一个类似于
dict
的接口,该接口指向包含pickled数据的数据库,如您在文档中的示例所示:所使用的数据库是
ndbm
或gdbm
,这取决于可用的平台和库。注意:如果数据未移动到其他平台,则此操作很有效。如果您想将数据库复制到另一台计算机上,那么
shelve
将无法正常工作,因为它无法保证将使用哪个库。在这种情况下,使用显式SQL数据库可能是最好的选择。相关问题 更多 >
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