# wend.templates

Readymade templates: counter filename patterns.

Part 3 of Future Paths observes that sized and unsized counters are the same few t-strings written again and again. `counter` writes them once::

```text
counter("log", width=5, suffix=".parquet")
# PathExpr('log_{idx:05d}.parquet')
counter("chunk", width=3, of_total=True, suffix=".parquet")
# PathExpr('chunk_{idx:03d}-of-{total:03d}.parquet')
```

A counter is an ordinary one-segment expression: join it below a directory, render it, match it, glob it. Its parameters are integers formatted with `d`, so matching parses them back as `int`, and a literal after each field that does not start with a digit keeps matching on its single-parse fast path.

## counter

```python
counter(
    stem: str = "",
    *,
    width: int | None = None,
    suffix: str = "",
    of_total: bool = False,
    sep: str = "_",
    of: str = "-of-",
    idx: str | Param = "idx",
    total: str | Param = "total",
) -> PathExpr
```

A counter filename: `{stem}{sep}{idx}{suffix}`, or, with `of_total`, `{stem}{sep}{idx}{of}{total}{suffix}` (a *sized* counter, which says how many there are).

`width` zero-pads every number to that many digits (`{idx:04d}`); without it they are unpadded (`{idx:d}`). `sep` is only written when there is a stem. `idx` and `total` name the parameters, or are `Param`s to use (declared `type=int` by default), so a declared default carries over: `counter("chunk", of_total=True, total=Param("total", type=int, default=10))`.