save Function
====================
The ``save`` function is designed to save an API key into your application's configuration or a designated storage mechanism. It ensures the API key is valid and prompts the user for input if the provided key is not valid or if no key is provided.

.. autofunction:: evdspy.save

Function Signature
------------------

.. autofunction:: evdspy.save

Parameters
----------
api_key : str, optional
    The API key to be saved. If not provided or if an invalid key is passed, the user is prompted to input a valid API key interactively.

Behavior and Errors
-------------------
The function checks if the provided `api_key` is a valid string. If the `api_key` is `None` or not a string, it attempts to set the API key through an interactive input method provided by `set_apikey_input()`.
This function should handle cases where:
- An API key is not provided, leading to an interactive input request.
- An invalid API key type is provided, prompting a type check and subsequent interactive input request.
The final step involves checking the validity of the API key with `check_apikey_and_then_save(api_key)`, which presumably implements further validation and storage mechanisms.

Example Usage
-------------
Here is how you might typically call this function:

.. code-block:: python
    # Example of saving an API key directly
    save("your_api_key_here")
    # Example when no API key is provided; this will trigger an interactive input prompt
    save()

This function is crucial for scenarios where secure and valid API key storage is necessary for the operation of your application, particularly in environments where configuration changes dynamically or where user input is required to initiate configuration.