FAQ: Doubly Linked Lists: Python - Adding to the Tail

This community-built FAQ covers the “Adding to the Tail” exercise from the lesson “Doubly Linked Lists: Python”.

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Pass the Technical Interview with Python

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Is there a reason to use if current_head != None for the if statements? Is this just done for clarity for those new to Python? Currently, doing an implicit conversion to bool (if current_head:) is marked as wrong by the exercise.

Yeah I had the same sort issue than you. I wanted to use if not current_head == None, and I have an error too.
I guess they choose the one most readable…Great to see the way you solved it.

I did it this way too!

If current_head is 0 the code block also runs. That checks for if current_head is a falsy value even the ones that are not None so if current_head could be a falsy value and not None and you don’t want the code block to run, then don’t use this form:
if current_head:
.

I think that checking the value against None should be changed, even PEP8 recommends using is/is not PEP 8 – Style Guide for Python Code | peps.python.org, yet in the ‘recommended’ solution it’s still equals/not equals sign.