mypy and sqlalchemy: error: Name 'sqlalchemy' is not defined

Question

I have the following function:

def _init_db() -> "sqlalchemy.orm.session.Session":
    engine = create_engine("sqlite:///my_db.db")
    Base.metadata.create_all(engine)

    # Creating Session
    from sqlalchemy.orm import sessionmaker
    Session = sessionmaker(bind = engine)
    session = Session()
    return session

Running mypy on the code gives me this error

error: Name 'sqlalchemy' is not defined

I tried with and without the quotes around sqlalchemy.orm.session.Session

How can I add type hints for sqlalchemy classes? What am I missing?

gonczor · Accepted Answer · 2019-01-31 11:08:04Z

1

In order to use type hints you have import what you are trying to return. In first example I am trying to define a function returning some sqlite3 stuff without importing sqlite3. After I do import this module everything works fine.

In [1]: def init_db() -> sqlite3.Connection:
   ...:     return sqlite3.connection
   ...:
   ...:
---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-1-b64a7629272c> in <module>()
----> 1 def init_db() -> sqlite3.Connection:
      2     return sqlite3.connection

NameError: name 'sqlite3' is not defined

In [2]: import sqlite3

In [3]: def init_db() -> sqlite3.Connection:
   ...:     return sqlite3.connection
   ...:
   ...:

In [4]:

answered Jan 31, 2019 at 11:08

gonczor

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2 Comments

langlauf.io Over a year ago

I added import sqlalchemy.orm.session.Session at the beginning of my script and got error: No library stub file for module 'sqlalchemy.orm.session.Session. So I guess there is no support for this class.

gonczor Over a year ago

Add import sqlalchemy at the top or annotate only Session instead of the full path.

langlauf.io · Accepted Answer · 2019-01-31 11:20:05Z

0

I got it thanks to gonczor's answer.

I needed to add

from sqlalchemy.orm.session import Session

at the beginning and then do

def _init_db() -> "Session":
    engine = create_engine("sqlite:///my_db.db")
    Base.metadata.create_all(engine)

    # Creating Session
    from sqlalchemy.orm import sessionmaker
    Session = sessionmaker(bind = engine)
    session = Session()
    return session

answered Jan 31, 2019 at 11:20

langlauf.io

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