What is the contextlib.ExitStack?

Question

Accepted Answer

**ExitStack** manages **multiple context managers** dynamically.

```python
from contextlib import ExitStack

# Open multiple files
with ExitStack() as stack:
    files = [
        stack.enter_context(open(f"file{i}.txt"))
        for i in range(5)
    ]
    for f in files:
        process(f)
    # All files closed automatically

# Dynamic context managers
from contextlib import contextmanager

@contextmanager
def managed_resource(name):
    print(f"Acquiring {name}")
    yield name
    print(f"Releasing {name}")

with ExitStack() as stack:
    resources = []
    for name in ["db", "cache", "queue"]:
        resource = stack.enter_context(managed_resource(name))
        resources.append(resource)
    process(resources)
    # All resources released in reverse order

# Callbacks
with ExitStack() as stack:
    stack.callback(print, "Cleanup 1")
    stack.callback(print, "Cleanup 2")
    # On exit: prints "Cleanup 2" then "Cleanup 1"
```

**Use cases:**
- Opening unknown number of resources.
- Dynamic context management.
- Cleanup callbacks.

Python: What is the contextlib.ExitStack?