Passing an SQLAlchemy Session to a TKinter controller - python-2.7

Question

I am currently learning how to work with the tkinter gui and I am trying to integrate with SQLAlchemy. The first hurdle was figuring out how to move between frames without destroying/closing the window, luckily I found this question: Switch between two frames in tkinter. So I used a lot of the provided code and created a simple application that is trying to have someone log in.
Now for the part I can't figure out. I have a function _check_credentials(self) deep inside the structure of windows that is trying to query the db. I have successfully created the table and queried it elsewhere.
I need to pass the session from the main.py module to the Login class and finally to the _check_credentials(self) method.
main.py -> Authorzation() -> Login() -> login_btn = tk.Button() -> _check_credentials()
Additional info:
I have included all of my code. Right now it runs, but crashes when the login button is pressed.
I have attempted to pass the session directly, ie. Authorzation(Session) but that crashes immediately.
Also, I am trying to follow the guidelines laid out in the sqlalchemy docs http://docs.sqlalchemy.org/en/latest/orm/session.html, FAQ, "When do I construct a Session, when do I commit it, and when do I close it?".
main.py:
from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker
from module1 import Authorzation
import Tkinter as tk
Base = declarative_base()
engine = create_engine('sqlite:///:memory:', echo=True)
Base.metadata.create_all(engine)
Session = sessionmaker(bind=engine)
session = Session()
app = Authorzation()
app.mainloop()
module1.py:
import Tkinter as tk
import user
TITLE_FONT = ("Helvetica", 18, "bold")
class Authorzation(tk.Tk):
def __init__(self, *args, **kwargs):
tk.Tk.__init__(self, *args, **kwargs)
# the container is where we'll stack a bunch of frames
# on top of each other, then the one we want visible
# will be raised above the others
container = tk.Frame(self)
container.pack(side="top", fill="both", expand=True)
container.grid_rowconfigure(0, weight=1)
container.grid_columnconfigure(0, weight=1)
self.frames = {}
for F in (Login, Register):
frame = F(container, self)
self.frames[F] = frame
# put all of the pages in the same location;
# the one on the top of the stacking order
# will be the one that is visible.
frame.grid(row=0, column=0, sticky="nsew")
self.show_frame(Login)
def show_frame(self, c):
'''Show a frame for the given class'''
frame = self.frames[c]
frame.tkraise()
class Login(tk.Frame):
def __init__(self, parent, controller):
self.controller = controller
tk.Frame.__init__(self, parent)
label = tk.Label(self, text="Title", font=TITLE_FONT)
label.pack(side="top", fill="x", pady=10)
#Create the Username field
label_username = tk.Label(self, text="username")
label_username.pack()
self.username = tk.StringVar()
tk.Entry(self, textvariable=self.username).pack()
#Create the password field
label_password = tk.Label(self, text="password")
label_password.pack()
self.password = tk.StringVar()
tk.Entry(self, textvariable=self.password).pack()
login_btn = tk.Button(self, text="Login",
command=self._check_credentials)
login_btn.pack(pady=5)
reg_btn = tk.Button(self, text="Registration",
command=lambda: controller.show_frame(Register))
reg_btn.pack(pady=10)
def _check_credentials(self):
session_user = session.query(user.User)\
.filter_by(
username=self.username
).first()
if session_user:
return session_user.check_pwd(), session_user
else:
print("Sorry we could not find your username")
return False, None
self.controller.show_frame(Login)
class Register(tk.Frame):
def __init__(self, parent, controller):
tk.Frame.__init__(self, parent)
label = tk.Label(self, text="This is page 1", font=TITLE_FONT)
label.pack(side="top", fill="x", pady=10)
button = tk.Button(self, text="Go to the start page",
command=lambda: controller.show_frame(Login))
button.pack()

Answer 1

After doing research on *args, and **kwargs. I realized I had not tried putting the session first in the __init__() function. Here is how I then passed the session to the controller.
main.py:
app = Authorzation(session)
module1.py
class Authorzation(tk.Tk):
def __init__(self, session, *args, **kwargs):
self.session = session
Once the session was in the controller it was easy to reference it from the Login() frame.
module1.py:
class Login(tk.Frame):
def __init__(self, parent, controller):
self.controller = controller
...
def _check_credentials(self):
session = self.controller.session
Note: this solution is also nice because it alleviates the need to pass the session through the button.