Answer:
See explanation
Explanation:
A “shelf” is a dictionary-like object. A shelf is an arbitrary Python objects, that is; anything that the pickle module can handle. This includes recursive data types and objects containing lots of shared sub-objects. It must be noted that the keys are ordinary strings.
(A). modification to Shelve can be done by following this instructions;
(1). Do not redefine built-in functions,(2). grab shelved item, mutate item, write mutated item back to shelf.
The number (2) instructions is during iteration over shelved items.
(B). CREATING FUNCTIONS THAT TAKES IN TWO SHELVES;
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!)
# 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
