def extract_vol(string):
    """Extracts the volume number from the information extracted from Zoobank

    Args:
        string (str): String being passed by the Item Pipeline

    Returns:
        str: String with the available volume
    """
    # Usually volume numbers immediatelly precedes '(' or ':'.
    # If, however, they are not present but we still have a number without '-'
    # or en-dash, this often means volume number
    # If none of these conditions are met, then, return empty string
    if '(' in string:
        return string[:string.find('(')]
    elif ':' in string:
        return string[:string.find(':')]
    elif '-' not in string and '–' not in string:
        return string
    else:
        return ''