How to import Scrapy item keys in the correct order?

Question

I am importing the Scrapy item keys from items.py, into pipelines.py. The problem is that the order of the imported items are differe

Answer 1

A simple fix is to define keys() method in your Item class:

class MyItem(Item):
    foo = Field()
    bar = Field()
    gar = Field()
    cha = Field()

    def keys(self):
        # in your preferred order
        return ['cha', 'gar','bar','foo']

Answer 2

The only way I could get this to work, was to use this solution in the following manner.

My items.py file:

from scrapy.item import Item, Field
from collections import OrderedDict
from types import FunctionType

class StaticOrderHelper(type):
    # Requires Python3
    def __prepare__(name, bases, **kwargs):
        return OrderedDict()

    def __new__(mcls, name, bases, namespace, **kwargs):
        namespace['_field_order'] = [
                k
                for k, v in namespace.items()
                if not k.startswith('__') and not k.endswith('__')
                    and not isinstance(v, (FunctionType, classmethod, staticmethod))
        ]
        return type.__new__(mcls, name, bases, namespace, **kwargs)

class NewAdsItem(metaclass=StaticOrderHelper):
    AdId        = Field()
    DateR       = Field()
    AdURL       = Field()

Then import the _field_order item into your piplines.py with:

...
from adbot.items import NewAdsItem
...
class DbPipeline(object):
    ikeys = NewAdsItem._field_order
    ...
    def createDbTable(self):
        print("Creating new table: %s" % self.dbtable )
        print("Keys in creatDbTable: \t%s" % ",".join(self.ikeys) )
        ...

I can now create new DB tables in the correct order of appearance, without worrying of Python's weird way of sorting dicts in unexpected ways.