"type" command in python gives unexpected results

Question

I ran the following code in the Python interpreter:

>>> s
<sqlalchemy.orm.session.Session object at 0x7f4fc8d69e10>
>>> type(s)
<class 'sqlalchemy.orm.session.Session'>
>>> type(s) == sqlalchemy.orm.session.Session
False

(1) Why does the interpreter say the type of s is not sqlalchemy.orm.session.Session, when it just said that it was?

(2) If the type command doesn't work, what is the best way to tell if an object is a Session object? (I'm trying to use this in an assertion to validate the input to a function)

(3) Just for fun, I tried to do this with a primitive type, and it worked. Why are integers different here?

>>> type(3)
<type 'int'>
>>> type(3) == int
True

It works for me. `s = orm.session.Session();type(s) == sqlalchemy.orm.session.Session -> True`, what does `isinstance(s, sqlalchemy.orm.session.Session)` output? — Padraic Cunningham, Jun 09 '16 at 23:14
You would be better off using isinstance anyway. http://stackoverflow.com/questions/1549801/differences-between-isinstance-and-type-in-python — Padraic Cunningham, Jun 09 '16 at 23:18
Did you `reload` any modules or do anything that might cause modules to be reloaded? — user2357112, Jun 09 '16 at 23:28
Aside: `type` is a function, not a command, in this context. — Charles Duffy, Jun 10 '16 at 00:41

score 2 · Accepted Answer · answered Jun 09 '16 at 23:43

Your s is actually an instance of a subclass of sqlalchemy.orm.session.Session. The subclass is confusingly also named sqlalchemy.orm.session.Session.

Looking at the SQLAlchemy source, it seems likely that this object was produced by a sqlalchemy.orm.session.sessionmaker, which creates a subclass of Session for reasons I'm not entirely clear on. I don't know if this behavior is documented; I didn't find any mention of it in the docs on a quick look.

"type" command in python gives unexpected results

1 Answers1