User-defined cache location

The location of the local storage cache in the users’ computer is usually hard-coded when we call pooch.create. There is no way for them to change it to something else.

To avoid being a tyrant, you can allow the user to define the cache location using an environment variable:

BRIAN = pooch.create(
    # This is still the default
    path=pooch.os_cache("plumbus"),
    base_url="https://github.com/rick/plumbus/raw/{version}/data/",
    version=version,
    version_dev="main",
    registry={
        "c137.csv": "19uheidhlkjdwhoiwuhc0uhcwljchw9ochwochw89dcgw9dcgwc",
        "cronen.csv": "1upodh2ioduhw9celdjhlfvhksgdwikdgcowjhcwoduchowjg8w",
    },
    # The name of an environment variable that can overwrite the path
    env="PLUMBUS_DATA_DIR",
)

In this case, if the user defines the PLUMBUS_DATA_DIR environment variable, Pooch use its value instead of path.

Pooch will still append the value of version to the path, so the value of PLUMBUS_DATA_DIR should not include a version number.