> ## Documentation Index
> Fetch the complete documentation index at: https://docs.sifr.sh/llms.txt
> Use this file to discover all available pages before exploring further.

# SIFR-STDLIB-0004: Standard-library cache build or reuse failure.

> Standard-library cache build or reuse failure.

`SIFR-STDLIB-0004` belongs to the **Standard library surface** diagnostic family. It means: standard-library cache build or reuse failure.

## Why It Happens

The selected standard-library surface is not supported in this form. Use the documented `sifr.*` contract for the API you need.

<Info>
  Use `sifr --explain SIFR-STDLIB-0004` locally to see the renderer's exact message template and any machine-applicable suggestions for the compiler version you are running.
</Info>

## Erroneous Code

```python theme={null}
values = defaultdict()
```

## How To Fix It

Use the supported `sifr.*` surface and constructor shape. Some CPython conveniences are intentionally absent or require explicit arguments.

## Fixed Code

```python theme={null}
from sifr.collections import defaultdict

values = defaultdict(lambda: 0)
```

## Details

| Field                  | Value                                                 |
| ---------------------- | ----------------------------------------------------- |
| Code                   | `SIFR-STDLIB-0004`                                    |
| Family                 | `STDLIB`                                              |
| Severity               | Error                                                 |
| Stability              | stable                                                |
| Owner                  | `sifr_driver::stdlib::cache`                          |
| Representative fixture | `crates/sifr_driver/src/tests/project_build_check.rs` |

See the [Error Codes index](/diagnostics/error-codes) for the complete catalog.