Overriding __len__ fails

[hewei100]

This is not working under 0.7.3

from pony.orm import *

db = Database('sqlite', ':memory:')

class Person(db.Entity):
    name = Required(str)
    team = Set('Team')

class Team(db.Entity):
    name = Required(str)
    members = Set(Person)
    
    def add(self, member):
        self.members.add(member)
        return self
        
    def count(self):
        return self.members.count()
        
    def __len__(self):
        return len(self.members)

db.generate_mapping(create_tables=True)

with db_session:
    team_boy = Team(name='Boy Team')
    # AttributeError: _vals_  in pony/orm/core.py, line 3098
    team_boy.add(Person(name='Bob')).add(Person(name='David'))
    print(team_boy.count())
    print(len(team_boy))

But after this patch, it works as expected

--- lib/python3.5/dist-packages/pony/orm/core.py.orig   2018-01-30 02:01:45.049469709 +0000
+++ lib/python3.5/dist-packages/pony/orm/core.py        2018-02-03 07:10:27.122080144 +0000
@@ -4099,7 +4099,9 @@
 
         if obj is None:
             with cache.flush_disabled():
-                obj = obj_to_init or object.__new__(entity)
+                obj = obj_to_init
+                if obj is None:
+                   obj = object.__new__(entity)
                 cache.objects.add(obj)
                 obj._pkval_ = pkval
                 obj._status_ = status

[stanislavkozlovski]

Yeah, wow.
Seems like the truthy evaluation of a class calls the __len__ method.

Here is the following code sample on Python 3.6

class TestClass:
    def __len__(self):
        print("LEN CALLED")
        return False

a = TestClass()
b = a or 1  # calls __len__
if a:  # calls __len__
  pass
else:
  print(b)

Output:

LEN CALLED
LEN CALLED
1

[sashaaero]

Hi! Thanks for reporting.
We've fixed it. Will be released soon.