What is an InstrumentedList in Python?

Question

During some set operations I encountered this error in Python:

TypeError: unhashable type: 'InstrumentedList'

What is an InstrumentedList in Python? I only found a few references related to SQLAlchemy. Is this a SQLAlchemy implementation of lists or something?

By the way, it happens while doing:

set(self.some_list)

where

print type(self.some_list) # <type 'list'>

Answer 1

Yes, SQLAlchemy uses it to implement a list-like object which is aware of insertions and deletions of related objects to an object (via one-to-many and many-to-many relationships).

Answer 2

Yes it's part of SQLAlchemy API. Here is the class reference:

http://docs.sqlalchemy.org/en/latest/orm/collections.html#sqlalchemy.orm.collections.InstrumentedList