Breaking changes v6.0.0: attribute comparison

[bram-tv]

The "breaking changes" list of v6.0.0 is missing a breaking change.

With PynamoDB v5.3.2 (and before) an equal check (==) on an attribute did an is check.
With PynamoDB v6.0.0 it returns a Comparison operator (which then fails in boolean context).

This change of behaviour was introduced in commit 163c75f for issue #508.

Sample code:

from pynamodb.models import Model
from pynamodb.attributes import UnicodeAttribute

class UserModel(Model):
    """
    A DynamoDB User
    """
    class Meta:
        table_name = 'dynamodb-user'
        region = 'us-west-1'
    email = UnicodeAttribute(hash_key=True)
    first_name = UnicodeAttribute()
    last_name = UnicodeAttribute()


field = UserModel.email

if field == UserModel.email:
    print("Email field")
else:
    print("Not the email field")

Running with PynamoDB v5.3.2:

Email field

Running with PynamoDB v6.0.0

Traceback (most recent call last):
  File ".....py", line 18, in <module>
    if field == UserModel.email:
  File ".../site-packages/pynamodb/expressions/condition.py", line 58, in __bool__
    raise TypeError("unsupported operand type(s) for bool: {}".format(self.__class__.__name__))
TypeError: unsupported operand type(s) for bool: Comparison

The fix for the sample code:

if field == UserModel.email:

should be replaced with:

if field is UserModel.email: