Disable leading underscore removal in attrs auto-generated init method signature

Question

attr strips leading underscore from attribute names for the generated __init__ method . Is there a way to override that for a particular attribute, short of disabling auto-generated initialization method for the class entirely?

I'd like to use attr class to represent MongoDB documents, which in Python are dictionaries with the _id key to record the unique id. I was hoping to be able to have a from_db(cls, doc) class method that's little more than return cls(**doc), but the presence of _id causes "TypeError: init() got an unexpected keyword argument '_id'". Right now, I work around it by declaring `_id: attr.ib(init=False, default=None), and having:

@classmethod from_db(cls, doc):
    _id = doc["_id"]
    del(doc["_id"])
    obj = cls(**doc)
    obj._id = _id
    return obj

but that seems really klugey. Is there a better way?

Answer 1

Currently not possible, sorry.

See:

• https://github.com/python-attrs/attrs/issues/391
• https://github.com/python-attrs/attrs/issues/619

Long-term you'll probably run into more complicated exceptions and then tools like cattrs make more sense.