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Overriding __len__ fails #331

hewei100 opened this issue Feb 3, 2018 · 2 comments

Overriding __len__ fails #331

hewei100 opened this issue Feb 3, 2018 · 2 comments


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hewei100 commented Feb 3, 2018

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):
        return self
    def count(self):
        return self.members.count()
    def __len__(self):
        return len(self.members)


with db_session:
    team_boy = Team(name='Boy Team')
    # AttributeError: _vals_  in pony/orm/, line 3098

But after this patch, it works as expected

--- lib/python3.5/dist-packages/pony/orm/   2018-01-30 02:01:45.049469709 +0000
+++ lib/python3.5/dist-packages/pony/orm/        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)
                 obj._pkval_ = pkval
                 obj._status_ = status

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stanislavkozlovski commented Feb 18, 2018

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__



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

@kozlovsky kozlovsky added this to the 0.7.4 milestone Mar 17, 2018
@kozlovsky kozlovsky added the bug label Mar 17, 2018
kozlovsky added a commit that referenced this issue Jul 23, 2018
# Major features

* Hybrid methods and properties added:
* Allow to base queries on another queries: `select(x.a for x in prev_query if x.b)`
* Added support of Python 3.7
* Added support of PyPy
* `group_concat()` aggregate function added
* pony.flask subpackage added for integration with Flask

# Other features

* `distinct` option added to aggregate functions
* Support of explicit casting to `float` and `bool` in queries

# Improvements

* Apply @cut_traceback decorator only when pony.MODE is 'INTERACTIVE'

# Bugfixes

* In SQLite3 `LIKE` is case sensitive now
* #249: Fix incorrect mixin used for Timedelta
* #251: correct dealing with qualified table names
* #301: Fix aggregation over JSON Column
* #306: Support of frozenset constants added
* #308: Fixed an error when assigning JSON attribute value to the same attribute: obj.json_attr = obj.json_attr
* #313: Fix missed retry on exception raised during db_session.__exit__
* #314: Fix AttributeError: 'NoneType' object has no attribute 'seeds'
* #315: Fix attribute lifting for JSON attributes
* #321: Fix KeyError on obj.delete()
* #325: duplicating percentage sign in raw SQL queries without parameters
* #331: Overriding __len__ in entity fails
* #336: entity declaration serialization
* #357: reconnect after PostgreSQL server closed the connection unexpectedly
* Fix Python implementation of between() function and rename arguments: between(a, x, y) -> between(x, a, b)
* Fix retry handling: in PostgreSQL and Oracle an error can be raised during commit
* Fix optimistic update checks for composite foreign keys
* Don't raise OptimisticCheckError if db_session is not optimistic
* Handling incorrect datetime values in MySQL
* Improved ImportError exception messages when MySQLdb, pymysql, psycopg2 or psycopg2cffi driver was not found
* desc() function fixed to allow reverse its effect by calling desc(desc(x))
* __contains__ method should check if objects belong to the same db_session
* Fix pony.MODE detection; mod_wsgi detection according to official doc
* A lot of inner fixes
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