liquidnitrogen - freeze arbitrary Python things as immutables

HOMEPAGE

https://github.com/mcandre/liquidnitrogen

PyPi

https://pypi.python.org/pypi/liquidnitrogen

EXAMPLES

Default argument immutables

Relax, you can now use collections directly in default arguments without any None checking.

>>> from liquidnitrogen import freeze

>>> def bad_append(value, lst=[]):
    lst.append(value)
    return lst

>>> train1 = bad_append('engine')
>>> train2 = bad_append('caboose', train1)

>>> train3 = bad_append('engine')
>>> train3
['engine', 'caboose', 'engine']

>>> def good_append(value, lst=freeze([])):
    return lst + (value,)

>>> train3 = good_append('engine')
>>> train4 = good_append('caboose', train3)

>>> train5 = good_append('engine')
>>> train5
('engine',)

Thread-safe immutables

Make complex objects thread-safe! Identify methods that are not thread-safe.

>>> sharable = freeze(SomeComplexThing())

>>> threads = [Actor(sharable) for i in range(10)]
>>> for thread in threads:
        thread.start()
...
liquidnitrogen.LiquidNitrogenException: frozenmethod call update with arguments ({'a', 1}) {} would mutate SomeComplexThing

freeze(list)

>>> collection = freeze([1, 2, 3])
>>> collection.append(4)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'tuple' object has no attribute 'append'
>>> collection
(1, 2, 3)

freeze(dict)

>>> collection = freeze({'a': 1, 'b': 2, 'c': 3})
>>> collection.update({'d': 4})
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'frozendict' object has no attribute 'update'
>>> collection
<frozendict {'b': 2, 'c': 3, 'a': 1}>

freeze(obj)

Freeze arbitrarily deep objects!

Warning: freezemethod and freezeobject perform a deepcopy of the object's attributes upon each method call in order to test whether the method call would modify the object. The attribute copy may use a significant amount of memory. To save memory, model data with structures designed to be immutable, such as tuples, frozensets, frozendicts, etc.

>>> class Person:
    def __init__(self, name):
        self.name = name
    def set_name(self, name):
        self.name = name
    def __eq__(self, other):
        return self.name == other.name
    def __repr__(self):
        return 'Person({0})'.format(self.name)
>>> p = freeze(Person('Alice'))
>>> p.name = 'Bob'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/andrew/Desktop/src/liquidnitrogen/liquidnitrogen/freeze.py", line 53, in __setattr__
    .format(name, self)
liquidnitrogen.LiquidNitrogenException: Cannot alter attribute name of frozenobject Person(Alice)
>>> p.set_name('Bob')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/andrew/Desktop/src/liquidnitrogen/liquidnitrogen/liquidnitrogen.py", line 76, in protected_method
    .format(method_name, obj)
liquidnitrogen.LiquidNitrogenException: frozenmethod call set_name with arguments ('Bob',) {} would mutate Person(Alice)
>>> p
Person(Alice)

freezemethod(obj, method_name)

Freeze specific methods on objects.

>>> from liquidnitrogen import frozenmethod
>>> class Pet:
    def __init__(self, breed, name):
        self.breed = breed
        self.name = name
    def set_breed(self, breed):
        self.breed = breed
    def set_name(self, name):
        self.name = name
    def __eq__(self, other):
        return self.breed == other.breed and self.name == other.name
    def __repr__(self):
        return 'Pet({0}, {1})'.format(self.breed, self.name)

>>> p = Pet('tabby', 'Cosmo')
>>> p.set_breed = frozenmethod(p, 'set_breed')
>>> p.set_breed('tiger')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/andrew/Desktop/src/liquidnitrogen/liquidnitrogen/liquidnitrogen.py", line 76, in protected_method
    .format(method_name, args, kwargs, obj)
liquidnitrogen.LiquidNitrogenException: frozenmethod call set_breed with arguments ('tiger',) {} would mutate Pet(tabby, Cosmo)
>>> p.set_name('FizzBuzz')
>>> p
Pet(tabby, FizzBuzz)

CREDITS

• freeze(dict) uses the frozendict library
• freeze(OrderedDict) uses the frozenordereddict library
• freeze(object) based on Andreas Nilsson's ActiveState recipe.

LICENSE

FreeBSD