Return a mapping containing an install scheme.

    ``scheme`` is the install scheme name. If not provided, it will
    return the default scheme for the current platform.

def get_paths(scheme=_get_default_scheme(), vars=None, expand=True):
    """Return a mapping containing an install scheme.

    ``scheme`` is the install scheme name. If not provided, it will
    return the default scheme for the current platform.
    """
    _ensure_cfg_read()
    if expand:
        return _expand_vars(scheme, vars)
    else:
        return dict(_SCHEMES.items(scheme))