Flask self.errors.append() - 属性错误：'tuple'对象没有'append'属性

Question

我这个小注册应用在尝试验证用户提交的数据时出错，特别是检查输入的电子邮件是否存在时。

这是我的文件：
表单：

from flask.ext.wtf import Form
from wtforms import TextField, BooleanField, PasswordField, TextAreaField, validators
from wtforms.validators import Required
from app import models

class RegisterForm(Form):
"""RegisterForm class needed for retrieving data from user"""
username = TextField('username', [validators.Length(min=3, max=50), validators.Required()])
email = TextField('email', [validators.Length(min=3, max=100), validators.Required()])
password = PasswordField('password', [validators.Required()])
age = TextField('age', [validators.Length(min=1, max=3), validators.Required()])
about_user = TextAreaField('about_user', [validators.Length(max=500)])
img_url = TextField('img_url')


def email_unique(self, email):
    if models.User.query.filter_by(email = email).first() != None:
        self.email.errors.append('This E-mail address is already in use. Please choose another one.') 
        return False

视图：

#!flask/bin/python
from app import app, db, lm
from flask import render_template, url_for, flash, g, redirect, session, request
from flask.ext.login import login_user, logout_user, current_user, login_required
from forms import LoginForm, RegisterForm, EditForm
from models import User

@app.route('/register', methods = ['GET', 'POST'])
def register():
    form = RegisterForm()
    #makes the username unique
    u_unique =  form.username.data
    u_unique = User.unique_username(u_unique)

    #validates email adress and checks if it already exists or not 
    form.email_unique(form.email.data)

    if form.validate_on_submit():
        user = User(
            u_unique,
            form.password.data, 
            form.email.data, 
            form.age.data, 
            form.about_user.data,
            form.img_url.data)
        db.session.add(user)
        db.session.commit()
        flash('Thank you for your registration')
        flash('Your username is: ' + str(u_unique))
        return redirect(url_for('login'))
    else:
        for error in form.errors:
            flash(error)

    return render_template('register.html',
        title = 'Registeration',
        form = form)

错误信息是：

Traceback (most recent call last) File <br> "/home/maksad/Desktop/faskMonkey/flask/lib/python2.7/site-packages/flask/app.py", line 1701, in __call__ return self.wsgi_app(environ, start_response) 
File "/home/maksad/Desktop/faskMonkey/flask/lib/python2.7/site-packages/flask/app.py", line 1689, in wsgi_app response = self.make_response(self.handle_exception(e)) 
File "/home/maksad/Desktop/faskMonkey/flask/lib/python2.7/site-packages/flask/app.py", line 1687, in wsgi_app response = self.full_dispatch_request() 
File "/home/maksad/Desktop/faskMonkey/flask/lib/python2.7/site-packages/flask/app.py", line 1360, in full_dispatch_request rv = self.handle_user_exception(e) 
File "/home/maksad/Desktop/faskMonkey/flask/lib/python2.7/site-packages/flask/app.py", line 1358, in full_dispatch_request rv = self.dispatch_request() 
File "/home/maksad/Desktop/faskMonkey/flask/lib/python2.7/site-packages/flask/app.py", line 1344, in dispatch_request return self.view_functions[rule.endpoint](**req.view_args) 
File "/home/maksad/Desktop/faskMonkey/app/views.py", line 92, in register form.email_unique(form.email.data) 
File "/home/maksad/Desktop/faskMonkey/app/forms.py", line 26, in email_unique
 self.email.errors.append('This E-mail address is already in use. Please choose another one.')
 AttributeError: 'tuple' object has no attribute 'append'

Answer 1

这个答案有点复杂。“errors”在创建Field类的时候是一个元组。

class Field(object):
    """
    Field base class
    """
    errors = tuple()
    

但是当调用validate方法时，它会把这个元组转换成一个列表。

def validate(self, form, extra_validators=tuple()):
    self.errors = list(self.process_errors)
    

所以你需要做的就是在调用validate_on_submit之后，紧接着调用你的email_unique函数，这样validate_on_submit就会调用表单的validate函数，并把错误转换成列表。

@app.route('/register', methods = ['GET', 'POST'])
def register():
    form = RegisterForm()
    #makes the username unique
    u_unique =  form.username.data
    u_unique = User.unique_username(u_unique)

    #validates email adress and checks if it already exists or 

    if form.validate_on_submit():
        form.email_unique(form.email.data)
        user = User(
            u_unique,
            form.password.data, 
            form.email.data, 
            form.age.data, 
            form.about_user.data,
            form.img_url.data)
        db.session.add(user)
        db.session.commit()
        flash('Thank you for your registration')
        flash('Your username is: ' + str(u_unique))
        return redirect(url_for('login'))
    else:
        for error in form.errors:
            flash(error)

    return render_template('register.html',
        title = 'Registeration',
        form = form)

Answer 2

tuples 是一种不可变的数据类型，这意味着你不能对它们进行切片或赋值。如果你需要处理的数据类型需要添加或删除值，建议使用列表（list）来代替：

>>> a = (1,2,3)
>>> a.append(2)
AttributeError: 'tuple' object has no attribute 'append'
>>> b = [1,2,3]
>>> b.append(2)
[1,2,3,2]

Answer 3

我刚好遇到这个问题。我觉得更好的回答是，在你给元素添加错误之前，应该先验证这些元素。验证的过程会把错误信息放到一个列表里，如果你在验证字段之前就修改了这个列表，等你验证的时候它会被覆盖掉。

所以，你需要重写你表单的验证方法，先调用父类的验证方法，然后再运行你的 email_unique 方法。

这样你就可以把视图中的 email_unique 移除了，因为它会成为你提交时验证的一部分。

Answer 4

这个 tuple 对象是不能直接添加元素的。你可以先把它转换成一个列表，用 list() 这个方法，然后在列表里添加元素，最后再把它转换回 tuple。具体操作可以参考下面的代码：

>>> obj1 = (6, 1, 2, 6, 3)
>>> obj2 = list(obj1) #Convert to list
>>> obj2.append(8)
>>> print obj2
[6, 1, 2, 6, 3, 8]
>>> obj1 = tuple(obj2) #Convert back to tuple
>>> print obj1
(6, 1, 2, 6, 3, 8)

希望这对你有帮助！