GoKawiilWhat a Python `for` loop is really doing once you stop hand-waving.
There are certain Python features that are so straightforward to use, you forget they are doing anything at all.
Consider for x in y .
You write a list, or a string, or a range, and Python politely hands you back one item at a time. No index variable and no bounds checks. Compared to i++ from C/C++ or forEach from JavaScript, Python's version just works.
For a long time, I treated for x in y as just a syntax that meant “loop over this thing,” and that was enough. Then I started building Memphis, my Python interpreter in Rust, and eventually I had to stop hand-waving and answer an extremely rude question:
What is a for loop actually doing?
It turns out the answer is both simpler and more involved than I expected.
The illusion
Let’s start with a tiny example.
for x in [10, 20, 30]: print(x)
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