[Sqlalchemy-tickets] Issue #3640: make_transient causes field values to disappear (zzzeek/sqlalchemy)

[zestyping <iss...@bi...>]

New issue 3640: make_transient causes field values to disappear
https://bitbucket.org/zzzeek/sqlalchemy/issues/3640/make_transient-causes-field-values-to

zestyping:

My intended use case was to retrieve a row from a table and add a modified copy of the row. Using SQLAlchemy, I expressed this as a query, followed by make_transient on the retrieved instance, modifying some properties on the instance, and then committing the new instance.

After this point the instance is in a mysterious state, in which calling make_transient on it makes the values of its properties disappear.  Attached is a minimal script that demonstrates the bug.

Expected output is:
```
x.value = 1
y.value = 1
y.value = 1
```

Actual output is:
```
sys.version = 3.5.0 (default, Sep 23 2015, 04:42:00) 
[GCC 4.2.1 Compatible Apple LLVM 7.0.0 (clang-700.0.72)]
sqlalchemy.__version__ = 1.0.11

x.value = 1
y.value = 1
y.value = None
```

Same in Python 2.7:
```
sys.version = 2.7.10 (default, Jul 14 2015, 19:46:27) 
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.39)]
sqlalchemy.__version__ = 1.0.11

x.value = 1
y.value = 1
y.value = None
```

Also, merely accessing y.value (see the script) changes the output, which is very suspicious behaviour.