What is a Python context manager?

Added: 2026-05-05

[00:00:00]A computer scientist spent years in the mid200s building a data set of over 14 million images while everyone else was chasing better algorithms. And in 2012, AlexNet proved her right. Now try loading 14 million images naively.

[00:00:14]You'll hit a problem really quickly. The whole thing crashes. Handling files at that scale forces a discipline that Python has a name for. The context manager. You've already used one. That width block guarantees that the file closes when you're done, even if something breaks. Without it, you're writing this same result, but much worse. And the pattern goes further than this. Databases, locks, timers, anything with a setup and a tearown. And here's one you may have used without even realizing it. Torch.nowgrad is a context manager. It turns off gradient tracking during inference and automatically restores it at the end of the block. So the same scale that made imageet hard to build makes context managers hard to avoid.