Iterate through class members in order of their declaration

python

Solution

It's possible in Python3, through the use of PEP3115 which allows you to override the dict type in the metaclass while the class is being constructed (eg. to use an OrderedDict which tracks the insertion order). Here's an implementation of this approach:

class OrderedMeta(type):
    @classmethod
    def __prepare__(metacls, name, bases): 
        return OrderedDict()

    def __new__(cls, name, bases, clsdict):
        c = type.__new__(cls, name, bases, clsdict)
        c._orderedKeys = clsdict.keys()
        return c

class Person(metaclass=OrderedMeta):
    name = None
    date_of_birth = None
    nationality = None
    gender = None
    address = None
    comment = None

for member in Person._orderedKeys:
    if not getattr(Person, member):
        print(member)

In Python2, it's a lot more tricky. It would be achievable with something fairly hacky like introspecting the source, and working out the definition order from the AST, but that's probably a lot more trouble than it's worth.

Problem

I got this problem writing a little GUI lib that maps classes to simple table views. Every class member of a certain type = column, and order of columns is important. But... ``` class Person(object): name = None date_of_birth = None nationality = None gender = None address = None comment = None for member in Person.__dict__.iteritems(): if not member[1]: print member[0] ``` output: ``` comment date_of_birth name address gender nationality ... ``` ugh, the oder got all mixed up...desired output: ``` name date_of_birth nationality gender address comment ``` Is there a way to do it without maintaining additional `OrderedDict()` of columns?

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