为什么正确设置 POST 方法后，我不断收到 405 错误（Method Not Allowed The method is not allowed for the requested URL.）？

Question

I am learning Flask and I've incurred into a supposedly beginners error:

Method Not Allowed The method is not allowed for the requested URL.

The thing is that, even though I reduce the code into something really simple, I can't find it. As far as I can see, the POST method is correctly set up (I will use comments to explain it).

The files are:

flaskblog.py

from flask import Flask, render_template, url_for, flash, redirect, request
from forms import RegistrationForm

app = Flask(__name__)
app.config['SECRET_KEY'] = '5791628bb0b13ce0c676dfde280ba245'

@app.route("/")
@app.route('/home', methods=['GET', 'POST']) # As one can see, the POST method is written there.
def home():
    form = RegistrationForm()
    return render_template('home.html', title='Home', form=form)

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

home.html

{% extends "layout.html" %}
{% block content %}
    <div class="content-section">
        <form method="POST" action=""> # The POST method is written there as well.
            {{ form.hidden_tag() }}
            <fieldset class="form-group">
                <legend class="border-bottom mb-4">Join Today</legend>
                <div class="form-group">
                    {{ form.username.label(class="form-control-label") }}
                    {{ form.username(class="form-control form-control-lg") }}
                </div>
            </fieldset>
            <div class="form-group">
                {{ form.submit(class="btn btn-outline-info") }}
            </div>
        </form>
    </div>
{% endblock content %}

forms.py

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

class RegistrationForm(FlaskForm):
    username = StringField('Username', validators=[DataRequired(), Length(min=2, max=20)])
    submit = SubmitField('Sign Up')

I get the error when I submit the form, any help would be greatly appreciated!

Thanks!

Answer 1

You're not distinguishing between GET and POST requests appropriately in your home route. Flask defaults the incoming request, from the client, as a GET request since your definitions are off. However, this is an issue because the incoming request is actually a POST request as we can see from your form:

<form method="POST" action=""> # The POST method is written there as well.

Perhaps you could try modifying your home route to handle both POST / GET requests approriately, something along the lines of:

@app.route("/")
@app.route('/home', methods=['GET', 'POST'])
def home():
    form = RegistrationForm()
    # POST request
    if form.validate_on_submit():
        return redirect(url_for(<route>)) #route to be rendered if form properly validates
    # GET request
    return render_template('home.html', title='Home', form=form)

Hopefully that helps!