TL;DR: Your script wants boto, the original AWS SDK for Python (v2), which is not installed. Quick fix: pip install boto. Real fix: migrate to boto3; boto is unmaintained.

```text
ModuleNotFoundError: No module named 'boto'
```

## Fix it

1. Stopgap: pip install boto. Expected: the import works.
2. Better: migrate to boto3. conn = boto.connect_s3() becomes boto3.client('s3'); bucket lookups become client.list_buckets(). Expected: modern, maintained code.
3. Verify: python -c "import boto3; print(boto3.__version__)". Expected: a version.
4. Update requirements: replace boto with boto3.

## When this applies
- The code does import boto (not boto3) and the package is missing.

## When it doesn't
- The code imports boto3: that is the modern package; install boto3.
- boto is installed but broken on Python 3.12+: boto v2 is unmaintained; migrate.

## Compatibility
- boto 2.49 is the last release; boto3 is current.

## Why it happens
Old tutorials, books, and vendored scripts predate boto3 (2015). New environments never include boto, so the import fails.

## Edge cases
- boto and boto3 coexist fine; migrating incrementally is safe.
- Some old boto code depends on Python 2 idioms; the migrate path forces cleanup.