# Cache

Utility for caching iterables.

This can be used to save a stream of data to the disk in order to iterate over it faster the following time. This can save time depending on the nature of the stream. The more processing happens in a stream, the more time will be saved. Even in the case where no processing is done apart from reading the data, the cache will save some time because it is using the pickle binary protocol. It can thus improve the speed in common cases such as reading from a CSV file.

## Parameters

- **directory**

  *Type* → `FilePath | None`

  *Default* → `None`

  The existing directory where to store the pickled data streams. If not provided, then a temporary directory is picked for the current system, and an exception is raised if none is known.

## Attributes

- **keys** (`set[str]`)

  The set of keys that are being cached.

## Examples

```python
import time
from river import datasets
from river import stream

dataset = datasets.Phishing()
cache = stream.Cache()
```

The cache can be used by wrapping it around an iterable. Because this is the first time we are iterating over the data, nothing is cached.

```python
tic = time.time()
for x, y in cache(dataset, key='phishing'):
    pass
toc = time.time()
print(toc - tic)  # doctest: +SKIP
```

```text
0.012813
```

If we do the same thing again, we can see the loop is now faster.

```python
tic = time.time()
for x, y in cache(dataset, key='phishing'):
    pass
toc = time.time()
print(toc - tic)  # doctest: +SKIP
```

```text
0.001927
```

We can see an overview of the cache. The first line indicates the location of the cache.

```python
cache  # doctest: +SKIP
```

```text
/tmp
phishing - 125.2KiB
```

Finally, we can clear the stream from the cache.

```python
cache.clear('phishing')
cache  # doctest: +SKIP
```

```text
/tmp
```

There is also a `clear_all` method to remove all the items in the cache.

```python
cache.clear_all()
```

## Methods

> [!NOTE]
>
> ****call****
>
> Iterates over a stream, caching it along the way if it is not cached yet.
>
> **Parameters**
>
> - **stream** — `Iterable[T]`
> - **key** — `str | None` — defaults to `None`

> [!NOTE]
>
> **clear**
>
> Delete the cached stream associated with the given key.
>
> **Parameters**
>
> - **key** — `str`

> [!NOTE]
>
> **clear\_all**
>
> Delete all the cached streams.