> ## 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-0001: Unsupported standard-library constructor, method, or surface.

> Unsupported standard-library constructor, method, or surface.

`SIFR-STDLIB-0001` belongs to the **Standard library surface** diagnostic family. It means: unsupported standard-library constructor, method, or surface.

## 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-0001` 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-0001`                                                            |
| Family                 | `STDLIB`                                                                      |
| Severity               | Error                                                                         |
| Stability              | stable                                                                        |
| Owner                  | `sifr_lowering::lower::builtin_calls`                                         |
| Representative fixture | `crates/sifr/tests/e2e/fail/defaultdict_keyword_constructor_unsupported.sifr` |

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