4. Saving objects to file

In the example below, shelve is shown as an alternative for storing multiple objects in one place.

Serialization choices become easier to maintain when the code states whether it is storing one value or a small keyed collection of values. Showing shelve alongside lower-level pickling makes that tradeoff more concrete for small local persistence tasks.

4.1. Don’t do this

import pickle

object_1 = 'pretend some big object 1'
object_2 = 'pretend some big object 2'
data = {
    'object_1': object_1,
    'object_2': object_2,
}

# write to file
pickle.dump(data, open('data.p', 'wb'))

# read from file
data = pickle.load(open('data.p', 'rb'))

4.2. Do this

import shelve

object_1 = 'pretend some big object 1'
object_2 = 'pretend some big object 2'

# write to file
with shelve.open('data') as s:
    s['object_1'] = object_1
    s['object_2'] = object_2

# read from file
with shelve.open('data') as s:
    print(s['object_1'])
    print(s['object_2'])