jsonstore
This module provides a class that maps keys and values from a JSON file onto its attributes.
The goal was to provide a convenient way of loading and saving configuration in a familiar human readable format. This is a bit more flexible than the configparser module which is included with Python.
This works is tested and working on Python 2.7+ and Python 3.3+. It will
not work on 2.6 or lower, but is expected to work on 3.0-3.2. The tests
do not work in 3.2.6 due to
mistreating
the
Examples
Basics
# by default JsonStore commits on every change unless in a transaction
store = JsonStore('config.json')
store.a_string = "something"
store.a_list = [1, 2, 3]
store.a_dictionary = {
'dict-list': [{}],
'ln(2)': 0.69314718056,
'for-you': u"💐",
}
# you can use […] to set/get/delete string keys
store['some_key'] = "a value"
# the key is split on '.'s and works on dictionaries
del store['a_dictionary.dict-list']
store['a_dictionary.new_value'] = "old value"
# you can also use the syntactic sugar for tuple keys (explicit lists work too)
assert store['a_dictionary', 'new_value'] == "old value"
# you can traverse lists too
assert store['a_list', -1] == 3
# you can use slices in lists
assert len(store['a_list', 1:]) == 2
del store['a_list', :2]
assert store.a_list == [3]
# deep copies are made when assigning values
my_list = ['fun']
store.a_list = my_list
assert store.a_list is not my_list
assert 'a_list' in store
# deep copies are also returned to avoid unsanitary changes being made
store.a_dictionary['new_value'] = "new value" # won't update the store!
assert store.a_dictionary['new_value'] == "old value"
assert store.a_dictionary is not store.a_dictionary
# Appending to, extending a list
>>> store.list = [1, 2, 3]
# Because of the fact that .append won't modify the list in the actual file,
# but only a copy...
>>> store.list.append(4)
>>> store.list
[1, 2, 3]
# ... we need to rather use the += operator to append to a list.
>>> store.list += [4]
>>> store.list
[1, 2, 3, 4]
# Similarly, we can extend the list
>>> store.list += [5, 6]
>>> store.list
[1, 2, 3, 4, 5, 6]Transactions
JsonStore objects can be used as context
managers to provide
transactions which are rolled back in the event of an exception. The
transaction model is primitive; you can only nest transactions.
While a store is put into a transaction, it will not save changes to file until all of the transactions have been closed.
from jsonstore import JsonStore
# even with auto_commit=True, the file won't be saved until the last contexts has been closed
with JsonStore('config.json', indent=None, auto_commit=False) as store:
self.value = 1
# the context manager will roll back changes made if an exception is raised
store = JsonStore('config.json', indent=None)
try:
with store:
store.value = "new"
raise Exception
except Exception:
pass
# here we see the value that was saved previously
assert store.value == 1
