Simple user registration in three styles

ball_of_mud.py

@expose('/register/', method=['POST']
def create_new_user():
  form = NewUserForm()
  
  username, password, email = form.data.username, form.data.password, form.data.email
  
  if User.query.filter_by(User.username == username).first():
    return {'success': False, 'reason': 'Username in use already'}
  
  elif User.query.filter(User.email == email).first():
    return {'success': False, 'reason': 'Email in use already'}
    
  else:
    password_hash = hash_password(password)
    user = User(username, password_hash, email)
    db.session.add(user)
    db.session.commit()
    return {'success': True, 'reason': None}

fauxo.py

@expose('/register/', method=['POST'])
def register_user():
  success, reason = form_to_new_user(NewUserForm())
  return {'success': success, 'reason': reason}
  
def form_to_new_user(form):
  username, password, email = form.data.username, form.data.password, form.data.email
  return register_user(username, password, email)
  
def register_user(username, password, email):
  all_users = User.query
  
  def on_create(username, password, email):
    password_hash = hash_password(password)
    user = User(username, password_hash, email)
    db.session.add(user)
    db.session.commit()
  
  created, reason = create_new_user(username, password, email, all_users, callback=on_create)
  return created, reason
  
def create_new_user(username, password, email, all_users, callback=None):
  if is_username_taken(username, all_users):
    return False, "Username in use already"
  elif is_email_taken(email, all_users):
    return False, "Email in use already"
  else:
    callback(username, password, email) if callback else None
    return True, ''
    
    
def is_username_taken(username, all_users):
  return any(username == user.username for user in all_users)
  
def is_email_taken(email, all_users):
  return any(email == user.email for user in all_users)

ports_and_adapters.py

@expose('/register/', method=['POST'])
def register_user():
  success, reason = form_to_new_user(NewUserForm(), app.repositories.get('user'))
  return {'success': success, 'reason': reason}

def form_to_new_user(form, user_repository):
  return create_new_user(user_repository, username, password, email)

def create_new_user(user_repository, username, password, email):
  if is_username_taken(username, user_repository):
    return False, "Username is in use"
  
  elif is_email_taken(email, user_repository):
    return False, "Email is in use"
    
  else:
    password_hash = hash_password(password)
    user = user_repository.create(username, password_hash, email)
    user_repository.save(user)
    return user, None
    
    
def is_username_taken(username, user_repository):
  return user_repository.first(username=username)

def is_email_taken(email, user_repository):
  return user_repository.first(email=email)