sqlalchemy query issue
user = User.query.get(1)
user.email = 'some@email.com'

if user.validate(): # The validate function performs a query to see if 'some@email.com' is already taken
        user.save()

check = User.query.filter_by(User.email='some@email.com').first()
if check:
        # email already exists

def user_email_exists(email):
    return (not User.query.filter(User.email=email) == None)

...

# User object to alter
user = ...

# the new email address, which needs to be checked
new_email_addr = 'new@shiny.com'

if user_email_exists(new_email_addr):
    raise SomeMeaningfulException() # or some `flash` message + a redirect
else:
    user.email = new_email_addr
    db.session.add(user)
    db.commit()

...