14.4 Shelves

Objects in dictionaries can be accessed by keys. There is a similar way to access particular data in a file by first assigning it a key. This is possible by using the module shelve:

from contextlib import closing
import shelve as sv
# opens a data file (creates it before if necessary)
with closing(sv.open('datafile')) as data:
    A = array([[1,2,3],[4,5,6]])     
    data['my_matrix'] = A  # here we created a key

In Section 14.1.1: Interacting with files, we saw that the built-in command open generates a context manager, and we saw why this is important for handling external resources, such as files. In contrast to this command, sv.open does not create a context manager by itself. The command closing from the module contextlib is needed to transform it into an appropriate context manager.

Consider the following example of restoring the file:

from contextlib import closing
import shelve...