# How to fix ImportError: cannot import name 'container_abcs' from 'torch._six'

The library importing torch._six is too old for your torch. `torch._six.container_abcs` was removed in torch 1.9; the modern equivalent is `collections.abc`. Upgrade the offending package (apex, pytorch-lightning, mmcv), or patch its import to `import collections.abc as container_abcs`. Your torch is fine; the caller is stale.

## The exact error

```text
ImportError: cannot import name 'container_abcs' from 'torch._six'
```

## Fix it

1. Read the traceback: find which file does `from torch._six import container_abcs` (often apex/amp/_amp_state.py or pytorch_lightning).
   Expected: you have the stale file path

2. Preferred: upgrade the stale package (`pip install -U [package]`, or reinstall apex from current master).
   Expected: the import line is gone or fixed upstream

3. If you must patch: replace `from torch._six import container_abcs` with `import collections.abc as container_abcs` and reinstall that package.
   Expected: import works on torch>=1.9

## When this applies

the traceback shows `from torch._six import container_abcs` failing on torch 1.9+

## When this does NOT apply

torch itself fails to import (DLL/shared-library errors) - that is an install problem, not this

## Versions

torch >= 1.9 with old apex / pytorch-lightning / mmcv

## Why it happens

torch removed the private _six compat module in 1.9; downstream libs pinned to the old private API.

## Edge cases

Downgrading torch below 1.9 'fixes' it too, but breaks everything else modern; upgrade the caller instead.