Alternative to Nested if statements Flask

Question

Summary

I have built a flask application thats taken several inputs from the user and the inputs need to be verified to certain criteria. If the inputs are not verified correctly, a flash message will show depicted what is incorrect of the input.

The home page has 4 nested if statements which displays certain messages based on the in correct result.

Python code

if request.method == 'POST':

        VM = request.form['email'] 
        RM = request.form['mobile']

        if isEmailInUse(VM):

            if VM not in blacklist and VM.endswith("@gmail.com"):

                if len(RM) == 11 and RM.startswith("555"):

                    create(user)

                    return redirect(url_for('see_users'))

                else:
                    flash('Invalid mobile! ', 'error')

            else:
                flash('Invalid Email Address! ', 'error')

        else:
            flash('Email Address already in use. ', 'error')

return render_template('Validate_Email.html')

I have tried

if VM not in blacklist and VM.endswith("@gmail.com"): flash('Invalid Email Address! ', 'error')

but it continues on with the code.

Is there an alternative to having so many nested ifs in flask to verify user input with flask messages?

some guidance or assistance would be much appreciated!

It's not good Python practice to write `a = b; x = y` on the same line of code afaik. — jarmod, Feb 16 '22 at 00:30

jarmod · Accepted Answer · 2022-02-18T01:32:39.300

2

Reverse the order of the tests and negate the logic, as needed, for example:

if request.method == 'POST':
    VM = request.form['email']
    RM = request.form['mobile']

    if not checkinUse(VM):
        flash('Email Address already in use. ', 'error')
    elif VM in blacklist or not VM.endswith("@gmail.com"):
        flash('Invalid Email Address! ', 'error')
    elif len(RM) != 11 or not RM.startswith("555")
        flash('Invalid mobile! ', 'error')
    else:
        create(user)
        return redirect(url_for('see_users'))

return render_template('Validate_Email.html')

PS checkinUse seems to be a questionable choice of name for a function that returns True if an email address is not in use.

edited Feb 18 '22 at 01:32

answered Feb 16 '22 at 00:35

jarmod

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Not sure why, sorry. I didn't downvote the question. On the `isEmailInUse` point - that function would ideally return True if the email address is in use, False if not in use and the first `if` test would then become `if isEmailInUse(VM)`. – jarmod Feb 16 '22 at 01:04
No problem well thank you for the assist it worked great! would you mind just editing the answer from 'elif if' to just 'elif' – Callum Feb 16 '22 at 01:08
Sorry, just noticed your request to fix the typo. Have fixed it. It's generally best to notify people e.g. `@jarmod` otherwise there's a good chance they will never see your comment. – jarmod Feb 18 '22 at 01:34

Alternative to Nested if statements Flask

Summary

Python code

1 Answers1