How to terminate a Python script

Question

I am aware of the die() command in PHP which exits a script early.

How can I do this in Python?

Answer 1

In Python 3.5, I tried to incorporate similar code without use of modules (e.g. sys, Biopy) other than what's built-in to stop the script and print an error message to my users. Here's my example:

## My example:
if "ATG" in my_DNA: 
    ## 
else: 
    print("Start codon is missing! Check your DNA sequence!")
    exit() ## as most folks said above

Later on, I found it is more succinct to just throw an error:

## My example revised:
if "ATG" in my_DNA: 
    ## 
else: 
    raise ValueError("Start codon is missing! Check your DNA sequence!")