cache.py

from abc import ABC, abstractmethod

class PickleCache(ABC):
    """Cache Python objects on disk to save on API calls

    Clients can treat this class like a key/value store. The fetch() method
    must be overridden to fetch a value from the API for a specific key.
    Then subclasses can be used as in this example:

        cache = SubclassedPickleCache(filepath)
        ...
        datum = cache.get(datum_key)
    """

    def __init__(self, cache_file_path: str) -> None:
        self.cache_file_path = cache_file_path
        self.updated = False
        self.data = {}
        if os.path.exists(self.cache_file_path):
            print(f"Opening cache file {self.cache_file_path}...")
            with gzip.open(self.cache_file_path, "rb") as fp:
                self.data = pickle.load(fp)
        else:
            self.updated = True

    @abstractmethod
    def fetch(self, key: Any) -> Any:
        """Fetch data about a given key from an API"""

    def get(self, key: Any) -> Any:
        """Get information about a given key"""

        if key not in self.data:
            self.data[key] = self.fetch(key)
            self.updated = True
        return self.data[key]

    def __del__(self) -> None:
        """Write the cache to disk, if necessary"""

        if self.updated:
            print(f"Saving cache to {self.cache_file_path}...")
            with gzip.open(self.cache_file_path, "wb") as fp:
                pickle.dump(self.data, fp)