Implementation of MP_API_KEY environment variable results in odd usage pattern

[bsjoelin]

The type annotations for MPRester states that api_key: str | None = DEFAULT_API_KEY. This is incorrect, since giving api_key = None fails with MPRestError stating "message":"No API key found in request".
This is due to api key then actually being None instead of the value of the MP_API_KEY environment variable, as one would expect.

So, when using MPRester inside functions, where you want to give the user the ability to give their API key as an optional argument you must give mp_api.client.mprester.DEFAULT_API_KEY as the default value. Thus, your code will end up looking something like this:

from typing import Optional
from mp_api.client import MPRester
from mp_api.client.mprester import DEFAULT_API_KEY

def function(arg1, arg2, ..., api_key: Optional[str] = DEFAULT_API_KEY):
    ...
    with MPRester(api_key) as mpr:
        ...

Instead of the more sensible choice that the type annotations suggest:

from typing import Optional
from mp_api.client import MPRester

def function(arg1, arg2, ..., api_key: Optional[str] = None):
    ...
    with MPRester(api_key) as mpr:
        ...

[munrojm]

@bsjoelin this is a sensible point. Thanks for the feedback. I will make the appropriate change.

[munrojm]

This should be fixed.