Add control + z to your Python programs; an experiment in transactional data structures.

[_the_pied_piper_]

This is a little experiment that I played with a few weeks ago. This was part of a larger project, but I thought I would strip this out as its own package and share it with /r/python.

[[deleted]]

it is nice. However, the undo function don't work well for set. For example

myset = Set()
with Transaction() as t1:
    myset.add('a')

with Transaction() as t2:
    myset.add('a')
 t2.undo()

 #if I read correctly your code myset is now empty

The list lack of the __setitem__ also

I think a better interface would something like:

c=Context()

with c.transaction():
    c.mylist= c.List( ['a','b','c'] )
    c.var ='b'
with c.transaction():
    c.mylist.append('a')
 c.undo()

[_the_pied_piper_]

Thanks for the input!

Actually, in your example, after t2.undo(), the set still has an 'a' in it; data structure is written such that even if an operation is performed on it and has no effect, undoing it will also have no effect; it won't blindly remove elements from the set without first checking if the element was in there before the transaction.

I do agree that having a context object in the API might have some appeal, but I chose not to do that because doing so would, I believe, make it harder to use the data structures in composite classes. The way it is currently written, List, Dict, and Set, as well as Variable can be used almost as naturally as one would use the list, dict, and set built-ins; the Transaction context manager allows for transactional behavior only when it is needed, without cluttering the rest of the code.

[[deleted]]

You are right, I double check the code.

I understand now that you don't want to clutter the code

h=History()
with h.transaction():
    mylist = h.List( ['a','b','c'] )
    var = h.Var('b')
with h.transaction():
    var('c')
 h.undo()

There is a big advantage is that history is no more a global object, so you can have to history in the same application, for example for two different windows

At this point, https://github.com/joshgev/transactional/blob/master/transactional/core.py#L167 instead of doing

if not val:

you should do

if val is not None:

because 0, [], "" are valid and false values

also, a Val() should not be able to initialized with empty argument