import pandas as pd


def convert_column_names(value):
    value = value.lower()
    value = value.replace(" ", "_")
    return value


def check_object(obj):
    if obj is None:
        raise ValueError('Return of yfinance download is None')
    elif isinstance(obj, pd.DataFrame):
        if obj.empty:
            raise ValueError('DataFrame is empty')
    else:
        raise ValueError(f'Return of yfinance download is neither a Dataframe nor None {type(obj)}')