14.1: The Two Species of Loops

Although some programming languages try to dress them up further, there are really only two fundamental kinds of loops in the world: fixed-iteration loops and variable-iteration loops.¹ The first kind is simpler to understand and less error-prone; in most languages (Python included) it is implemented as a “for loop.” The tricker, second kind is available to programmers as a “while loop.”

Happily for us, it turns out that while loops don’t come up much in Data Science, at least in the beginning. There are some more advanced techniques that use them (for instance, optimization methods and threshold detection) but for us it’s going to be for loops that dominate the landscape. So let’s figure out how they work.

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