attrsJSONCodec.py

import attr
from datetime import datetime
from attr import fields

@attr.s(slots=True)
class Small:
    a = attr.ib(type=float, metadata={'JSON':'A'})

@attr.s(slots=True)
class TestField:
    a = attr.ib(type=int, metadata={'JSON':'A'})
    b = attr.ib(type=datetime, metadata={"JSON":"B"}) 
    c = attr.ib(type=str, metadata={'JSON':'C'})
    d = attr.ib(type=Small, metadata={'JSON':'D'})

x = TestField(1,datetime.now(),"123",Small(1))
attr.asdict(x)

def fromJSON(dikt, cls):
    attrs = fields(cls)
    vals = {}
    for a in attrs:
        jname = a.metadata['JSON']
        v = dikt[jname]
        if attr.has(a.type):
            vals[a.name] = fromJSON(v, a.type)
        elif a.type in (tuple, list, set):
            # Get child type 
            mem_type = a.metadata['MemType']
            vals[a.name] =[ fromJSON(i, globals()[mem_type]) for i in v]
        elif a.type == datetime:
            vals[a.name] = datetime.now()
        else:
            vals[a.name] = v
    return cls(**vals)

def asJSON(inst, recurse=True, filter=None, dict_factory=dict,
           retain_collection_types=False):
    attrs = fields(inst.__class__)
    rv = dict_factory()
    for a in attrs:
        v = getattr(inst, a.name)
        jname = a.metadata['JSON']
        if jname is None: continue
        if filter is not None and not filter(a, v):
            continue
        if recurse is True:
            if attr.has(v.__class__):
                rv[jname] = asJSON(v, recurse=True, filter=filter,
                                    dict_factory=dict_factory)
            elif isinstance(v, (tuple, list, set)):
                cf = v.__class__ if retain_collection_types is True else list
                rv[jname] = cf([
                    asJSON(i, recurse=True, filter=filter,
                           dict_factory=dict_factory)
                    if attr.has(i.__class__) else i
                    for i in v
                ])
            elif isinstance(v, datetime):
                rv[jname] = str(v)
            elif isinstance(v, dict):
                df = dict_factory
                rv[jname] = df((
                    asJSON(kk, dict_factory=df) if attr.has(kk.__class__) else kk,
                    asJSON(vv, dict_factory=df) if attr.has(vv.__class__) else vv)
                    for kk, vv in v.iteritems())
            else:
                rv[jname] = v
        else:
            rv[jname] = v
    return rv