Python's None: Null in Python (Overview)

Thanks for the video..!

This was all very helpful. So thank you.

But it has confused me about something I had thought I understood.

I use if var: a lot to test if data exists. And I’m usually basing that on a returned function.

e.g.

def main(input):
    test = test_func(input)
    if test:
        do_something()
    else:
        do_something_else()

def test_func(input):
    if input == something:
        return something

Is it wrong of me, then, to use this Truthy/Falsey if test: approach? My test_func is returning None if the condition is not met, and so I want my main func to do_something_else().

To ensure this, would I be better writing if test is not None: instead?

Using explicit comparison is more Pythonic because it clearly states your intent. That’s one of the core philosophies you’ll find in the Zen of Python.

More importantly, however, relying on implicit truthy/falsy values is risky because it may not work as expected, depending on what your functions return. For example, if zero (0) should be considered a success, which often is in Unix programs, then your condition won’t work, because zero evaluates to false in a Boolean context.

As a rule of thumb, use explicit comparison whenever possible.

By the way, it’s also worth noting to avoid double negation in expressions like this:

if test is not None:
    success()
else:
    failure()

You can swap the order to make it a little easier on the eyes:

if test is None:
    failure()
else:
    success()