werkzeug.routing.BuildError: Could not build url for endpoint 'success'. Did you forget to specify values ['name']?

Question 1

"werkzeug.routing.BuildError: Could not build url for endpoint 'success'. Did you forget to specify values ['name']?"

How to solve this error? I have tried many things but can't solve it by myself.

http_methods.py:

from flask import Flask, redirect, url_for, request
app = Flask(__name__)

@app.route('/success/<name>')
def success(name):
    return 'welcome %s' % name

@app.route('/login', methods=['POST', 'GET'])
def login():
    if request.method == 'POST':
        user = request.form['nm']
        return redirect(url_for('success', name = user))
    else:
        user = request.args.get('nm')
        return redirect(url_for('success', name = user))

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

I get an error in the login method, that value of ['name'] is not specified; how to solve this error?

login.html:

<!DOCTYPE html>
<html lang="en">
    <body>
        <form action="http://127.0.0.1:5000/login" method="POST">
            <p>Enter name:</p>
            <p><input type="text" name="nm" value="nm"/></p>
            <p><input type="submit" value="submit"/></p>    
        </form>
    </body>
</html>

output:

  File "/Users/chirag.kanzariya/pythonprojects/v_python/lib/python3.7/site-packages/flask/helpers.py", line 345, in url_for
    force_external=external)
  File "/Users/chirag.kanzariya/pythonprojects/v_python/lib/python3.7/site-packages/werkzeug/routing.py", line 1776, in build
    raise BuildError(endpoint, values, method, self)
werkzeug.routing.BuildError: Could not build url for endpoint 'success'. Did you forget to specify values ['name']?
127.0.0.1 - - [29/Jan/2019 14:48:00] "GET /login?__debugger__=yes&cmd=resource&f=style.css HTTP/1.1" 200 -
127.0.0.1 - - [29/Jan/2019 14:48:00] "GET /login?__debugger__=yes&cmd=resource&f=jquery.js HTTP/1.1" 200 -
127.0.0.1 - - [29/Jan/2019 14:48:00] "GET /login?__debugger__=yes&cmd=resource&f=debugger.js HTTP/1.1" 200 -
127.0.0.1 - - [29/Jan/2019 14:48:00] "GET /login?__debugger__=yes&cmd=resource&f=ubuntu.ttf HTTP/1.1" 200 -
127.0.0.1 - - [29/Jan/2019 14:48:00] "GET /login?__debugger__=yes&cmd=resource&f=console.png HTTP/1.1" 200 -
127.0.0.1 - - [29/Jan/2019 14:48:00] "GET /login?__debugger__=yes&cmd=resource&f=console.png HTTP/1.1" 200 -

I am using python 3.7 and flask 1.0.2 version right now.

Question 2

Have a look at this. In your login function I added a render_template for the first GET request when opening the login page. This will probably also prevent the error you're getting now. Bear in mind this does not contain any error handling, like what happens if user is unknown in your login procedure.

@app.route('/success/<name>')
def success(name):
    return 'welcome %s' % name

@app.route('/login', methods=['POST', 'GET'])
def login():
    if request.method == 'POST':
        user = request.form['nm']
        return redirect(url_for('success', name = user))

    return render_template(login.html)

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

werkzeug.routing.BuildError: Could not build url for endpoint 'success'. Did you forget to specify values ['name']?

Mangs

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Mangs