None of the time differences in all the test cases are significant at all. Concerning yourself with this is premature optimization of the highest level especially in a language like Python. One should definitely be more concerned about writing clearer and more idiomatic code.
It reminds me a bit of some of my big data jobs. Sometimes you spend days and days torturing data to find interesting aspects, only to find nothing and end in "failure". Only it isn't failure because you've eliminated a bunch of dead-end avenues that you might otherwise have wondered about, freeing you to pursue more promising uses for your resources.
And while the individual differences are small, in a language already as slow as Python, starting from the faster, idiomatic code from the start is likely to save a lot of headache down the line.
There are also a few exceptions (the update() method on a dict and list comprehensions).
As a junior python dev < me < senior python dev, this was very cool to read, also very quick to take in, kuddos on the presentation
Python is a language about readability and conciseness first, performance second.
I would have liked to have seen `map` used in the list comp examples, as well as seeing the tests run on Python 3.
Not all optimization is premature. Sometimes you find that you do need to optimize, and then having to wade through a morass of comments complaining about premature optimization to track down actual relevant content and comment is a pain in the arse.