Python form.validate_on_submit() always false

Question

I'm using flask_wtf

this is my login form

from flask_wtf import FlaskForm
from wtforms import StringField, PasswordField, BooleanField, SubmitField
from wtforms.validators import DataRequired, Length


class LoginForm(FlaskForm):
    username = StringField('Username', validators=[DataRequired()])
    password = PasswordField('Password', validators=[DataRequired(), Length(8, 128)])
    remember = BooleanField('Remember me')
    submit = SubmitField('Log in')

and this is my login.html:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>login</title>
</head>
<body>
<form method="POST" action="">
    {{ form.csrf_token }}
    {{ form.username.label }}<br>{{ form.username }}<br>
    {{ form.password.label }}<br>{{ form.password }}<br>
    {{ form.remember }}{{ form.remember.label }}<br>
    {{ form.submit }}<br>
</form>
</body>
</html>

and my app.py

from flask import Flask, render_template
from forms import LoginForm

app = Flask(__name__)
app.secret_key = 'learnflask'
@app.route('/login', methods=['GET', 'POST'])
def login():
    form = LoginForm()
    if form.validate_on_submit():
        username = form.username.data
        print(username)
    return render_template('login.html', form=form)


if __name__ == '__main__':
    app.run(debug=True)

my problem is the username does not print . it seems the loginform not be submited,form.validate_on_submit() is false.

i make a mistake the password min length is 8

Oane
– Oane

2019-05-20 07:53:32 +00:00
Commented May 20, 2019 at 7:53 — Oane
– Oane, Commented May 20, 2019 at 7:53

arshovon · Accepted Answer · 2019-05-20 07:56:43Z

For password field the you have set validator to check if the length is between 8 and 128. If the user gives a password with smaller or larger length the validation will be failed. I think this is the reason why form.validate_on_submit() is always false.

I have shown the error message in the template and got the error.

login.html:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>login</title>
    <style>
        .validation_error{
        color: red;
    }
    </style>
</head>
<body>
<form method="POST" action="">
    {{ form.csrf_token }}
    {{ form.username.label }}<br>{{ form.username }}<span class="validation_error">{{ ', '.join(form.username.errors) }}</span><br>
    {{ form.password.label }}<br>{{ form.password }}<span class="validation_error">{{ ', '.join(form.password.errors) }}</span><br>
    {{ form.remember }}{{ form.remember.label }}<span class="validation_error">{{ ', '.join(form.remember.errors) }}</span><br>
    {{ form.submit }}<br>
</form>
</body>
</html>

app.py:

from flask import Flask, render_template
from forms import LoginForm

app = Flask(__name__)
app.secret_key = 'learnflask'
@app.route('/login', methods=['GET', 'POST'])
def login():
    form = LoginForm()
    if form.validate_on_submit():
        username = form.username.data
        return username
    return render_template('login.html', form=form)

Output:

Valid input:

Invalid input:

prashant · Accepted Answer · 2019-05-20 07:20:25Z

0

form.validate_on_submit() is false because you haven't added request.form object to LoginForm()

form = LoginForm(request.form)

answered May 20, 2019 at 7:20

prashant

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