def replace(df, replace_dict):
    """Replaces values in columns based on a dict

    Args:
        df (`pandas.DataFrame`): The dataframe to replace values in
        replacement_dict (dict): A dict containing columns, the values to replace, and what to replace them with.
            Should be formatted like:
            {
                'column_a': {'$': '', ',':''},
                'column_b': {'bought': 1, 'sold': -1}
            }
    """
    return df.replace(replace_dict)