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creates the next immutable object by simply modifying the current one

Project description


Create the next immutable object by simply modifying the current one

This is a Python port of immer.

pip install immerframe

Want to do a deep update on a Python data structure without mutating it? No problem:

from immerframe import Proxy, produce

Ant = namedtuple('Ant', 'age')
nested = {
    'foo': [

proxy = Proxy()
proxy['foo'][0].age += 1
proxy['qux'] = 99

new_nested = produce(proxy, nested)

new_nested will now equal

    'foo': [
    'qux': 99,

while nested will remain unchanged.

"What about my typing?"

from typing import cast

Cat = namedtuple('Cat', 'name')

proxy = cast(Cat, Proxy())
# continue as before but with autocomplete and type checking! = 'Felix'

immerframe uses structural sharing, so should be efficient in most cases:

d = {'foo': 1}
l = [d]

proxy = Proxy()
new_l = produce(proxy, l)
assert new_l == [d, 100]
assert new_l[0] is d

immerframe supports:

  • dicts
  • lists
  • sets
  • tupless
  • namedtupless
  • attrss


immerframe comes with a Lens class to help with path reuse, it has .get, .set, .modify:

d = {'foo': [1, 2, 3, 4]}

lens = Lens(Proxy()['foo'][1])

new_d = lens.set(d, 100)
assert new_d == {'foo': [1, 100, 3, 4]}
assert d == {'foo': [1, 2, 3, 4]}
assert lens.get(d) == 2

another_d = lens.modify(d, lambda n: n + 1000)
assert another_d == {'foo': [1, 1002, 3, 4]}

Lenss are composable via their .proxy() method, (this duplicates of the originally provided proxy) Lens(Lens(Proxy()['foo']).proxy()[1]) is equivalent to Lens(Proxy()['foo'][1]).


immerframe currently has an attrs plugin, registering plugins is pretty easy, just mutate the immerframe.plugins list (see here for the structure of the existing attr plugin).

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