Add check for base_score in _get_attributes function

[tolleybot]

In the _get_attributes function in xgboost/_parse.py, I've added a check for the base_score attribute. This change is necessary because base_score can sometimes be stored as a string, which can cause issues in subsequent computations that expect it to be a float.

The updated code now checks if base_score is not in kwargs and, if not, sets it to 0.5. If base_score is in kwargs and is a string, it converts it to a float.

Here's the updated code:

if 'base_score' not in kwargs: kwargs['base_score'] = 0.5 elif isinstance(kwargs['base_score'], str): kwargs['base_score'] = float(kwargs['base_score']) return kwargs

This change ensures that base_score is always a float, which should prevent potential type-related errors in the future.

[xadupre]

Closed, replaced by #637.