2008/11/4 Greg Ewing <greg.ewing@canterbury.ac.nz>:

Zaur Shibzoukhov wrote:

...

_p__0=['foo',None] _p__0[1]=_p__0 _p__0

It would be nice if it could be made a bit more declarative, such as:

_p__0=['foo',_p__0]

-- Greg

I implemented a rough version of dumps for fun on sunday, and I decided to let recursive / mutually recursive object be represented in this manner. Here are some examples below. >>> print dumps([1, 2, 1]) [1, 2, 1] Recursive objects are represented 'declaratively' >>> x = [1, 2] >>> y = [x, 'a', x] >>> print dumps(y) sym0 = [1, 2] [sym0, 'a', sym0] Mutually recursive objects also: >>> x.append(y) >>> print dumps((x, y)) sym0 = [1, 2, sym1] sym1 = [sym0, 'a', sym0] (sym0, sym1) Some examples with dictionaries >>> d = {'foo': (1, 2)} >>> print dumps(d) {'foo': (1, 2)} >>> d['me'] = d >>> print dumps(d) sym0 = {'me': sym0, 'foo': (1, 2)} sym0 An example with a class >>> class A(object): pass ... >>> a = A() >>> a.my = 'spam' >>> a.oh = (3, a) >>> print dumps(a) sym0 = A(my='spam', oh=(3, sym0)) sym0 Implementing this gave me the idea of extending it to representing object 'given' some definition. E.g. given that a='hello', then ['hello', 'world'] can be represented as [a, 'world']. This could be useful as when 'pickling' an object sometimes you end up pickling a lot of the state of the program, which is not necessary as you know it will not vary. Or sometimes you would like to pickle something 'modulo' some state. E.g. >>> print dumps(['hello', 'world'], a='hello') [a, 'world'] For hashable types, equal objects will be factored: >>> t = (1, 2) >>> print dumps(((1, 2), (1, 2)), u=(1, 2)) (u, u) >>> print dumps((t, (1, 2)), u=(1, 2)) (u, u) For non hashable types, this is not the case unless the objects are actually the same object: >>> l = [1, 2] >>> print dumps((l, l), mylist=l) (mylist, mylist) >>> print dumps((l, [1, 2]), mylist=l) (mylist, [1, 2]) One last example: >>> a = 3 >>> b = [1, 2] >>> class C(object): pass ... >>> c = C() >>> c.x = a, b >>> b.append(c) >>> print dumps(c) sym0 = C(x=(3, [1, 2, sym0])) sym0 >>> c.y={a:b} >>> print dumps(c) sym0 = C(y={3: sym1}, x=(3, sym1)) sym1 = [1, 2, sym0] sym0 >>> print dumps(b) sym0 = [1, 2, C(y={3: sym0}, x=(3, sym0))] sym0 >>> print dumps(b, c=c) [1, 2, c] -- Arnaud