Flask Internal Server Error but no error log - flask

Question

I am new to flask and tried to run this simple code from GeeksForGeeks
form.html
<form action="{{ url_for("gfg")}}" method="post">
<label for="firstname">First Name:</label>
<input type="text" id="firstname" name="fname" placeholder="firstname">
<label for="lastname">Last Name:</label>
<input type="text" id="lastname" name="lname" placeholder="lastname">
<button type="submit">Login</button>
flask_text.py
# importing Flask and other modules
from flask import Flask, request, render_template
# Flask constructor
app = Flask(__name__)
# A decorator used to tell the application
# which URL is associated function
#app.route('/', methods =["GET", "POST"])
def gfg():
if request.method == "POST":
# getting input with name = fname in HTML form
first_name = request.form.get("fname")
# getting input with name = lname in HTML form
last_name = request.form.get("lname")
return "Your name is "+first_name + last_name
return render_template("form.html")
if __name__=='__main__':
app.run()
https://www.geeksforgeeks.org/retrieving-html-from-data-using-flask/
You can find the code in the above link
I added app.debug = True but got no error log
I have my html file in /templates folder

Answer 1

First, The indentation of your code is wrong. Try this:
# importing Flask and other modules
from flask import Flask, request, render_template
# Flask constructor
app = Flask(__name__)
# A decorator used to tell the application
# which URL is associated function
#app.route('/', methods =["GET", "POST"])
def gfg():
if request.method == "POST":
# getting input with name = fname in HTML form
first_name = request.form.get("fname")
# getting input with name = lname in HTML form
last_name = request.form.get("lname")
return "Your name is "+first_name + last_name
return render_template("form.html")
if __name__=='__main__':
app.run()
Second, is your virtual environment running? (Can you see '(env)' at the start of your command line?)
If not, you need to first execute:
source env/bin/activate
and then pip3 install flask
If it still does not work, give me some more context.