How do you use multiple context managers at once?

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Accepted Answer

Three approaches:

1. **One `with`, comma-separated:** `with open('a') as a, open('b') as b:`. Both are entered left-to-right and exited in **reverse** order; each is cleaned up even if a later one or the block raises. Since Python 3.10 you can wrap them in **parentheses** for clean line-wrapping across multiple lines.
2. **`contextlib.ExitStack`** — when the number of context managers is **dynamic** (e.g. open a variable list of files). You `enter_context(cm)` in a loop; the stack guarantees all of them are unwound (in reverse) on exit. It also lets you transfer cleanup ownership (`pop_all`).
3. Nested `with` blocks — functionally equivalent but more indentation; the single-`with` form is preferred for a fixed set.

The guarantee is the same as a single context manager: every entered manager's `__exit__` runs, in reverse order, no matter how the block ends.

**Interview tip:** mention both the comma form (with the 3.10 parenthesized syntax) for a *fixed* set and **`ExitStack`** for a

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