app.py

from flask import Flask, render_template, request
app = Flask(__name__)

# Try to print this out to you
flag = "flag{nice_you_won_:3}"
# If you get that, try to print out flag.txt
# HINT: If you get an error or debug page, read what it says
# HINT: you will have to use subprocess:
# http://stackoverflow.com/questions/4760215/running-shell-command-from-python-and-capturing-the-output

@app.route('/', methods=['GET', 'POST'])
def do_thing():
    if request.method == 'POST':
        out = eval(request.form["runme"])
        return render_template('index.html', output=out)
    else:
        return render_template('index.html', output=None)

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