Why does the function not see the variable?

Question

Python

def actions():
    global flash
    node_name = request.args.get('node_name')
    if node_name:
        form = AddForm(obj = get_node_values(node_name))
        check = True
        return render_template('actions.html', form = form)
    form = AddForm()
    if request.method == 'POST' and form.validate_on_submit():
        operator = form.operator_name.data.lower()
       db_values = models.node(operator_name = operator, node_name = node,\
        node_id = nod_id)
        current_page = request.form['current_page']
        if check:
            flash(change_value_in_db(db_value))
            return redirect(url_for('actions'))

When trying to execute the condition block if check, an exception occurs:

local variable 'check' referenced before assignment

. I don’t understand why it can occur, because the variable is checkdeclared and processed in one function (there is a suspicion that this situation is due to branching, so Google is for help, but if anyone here knows, please tell me)
Thank you

Answer 1

checkdeclared only if if node_name:otherwise remains undeclared.

Answer 2

global is bad practice
and no CODE is "even worse"

def actions():
    global flash
    node_name = request.args.get('node_name')
    if node_name:
        form = AddForm(obj = get_node_values(node_name))
        check = True
        return render_template('actions.html', form = form)

    form = AddForm()
    if request.method == 'POST' and form.validate_on_submit():
        operator = form.operator_name.data.lower()
        db_values = models.node(operator_name = operator, node_name = node,\
                                                            node_id = nod_id)
        current_page = request.form['current_page']
        if check:
            flash(change_value_in_db(db_value))
    return redirect(url_for('actions'))

Answer 3

following good advice:

def actions():
    global flash
    node_name = request.args.get('node_name')
    if node_name:
        form = AddForm(obj = get_node_values(node_name))
        check = True
        return render_template('actions.html', form = form)
    form = AddForm()
    if request.method == 'POST' and form.validate_on_submit():
        operator = form.operator_name.data.lower()
        node = form.node_name.data.lower()
        nod_id = form.node_id.data.lower()
        db_values = models.node(operator_name = operator, node_name = node,\
        node_id = nod_id)
        current_page = request.form['current_page']
        if check:
            flash(change_value_in_db(db_value))
            return redirect(url_for('actions'))
        flash(add_value_in_db(db_values))
        return redirect(url_for('actions'))