Question

What is the correct way to show an operation has failed in python. In this code what should the return values be?

def compare(y,x):
     if y ==  x:
         return 'true'
     return 'false'

Answer 1

Python has literal values True and False which you can use. However, it’s rarely necessary to use them explicitly, as comparison operations will return one or the other value in most cases. For instance, you could redo your function to be:

def compare(y, x):
    return y == x

It’s also worth noting that non-Boolean values can be considered “true” or “false”, if necessary. The “falsy” values are None, 0 and all empty containers (such as the empty string '', the empty list [], the empty tuple (), the empty dictionary {} and so on). Everything else is “truthy” by default, including all instances of most kinds of objects.

Custom classes can have a boolean conversion defined by implementing the magical method __nonzero__ (which is renamed to __bool__ in Python 3). If it doesn’t exist, Python will check for __len__, and if that doesn’t exist give up and assume all instances are true.