def format_tag(tag):
    """
    Splits tags on ':' and removes enclosing quotes if present and returns
    returns both sides of the split as strings

    Example:
    >>> format_tag('user:foo')
    'user', 'foo'
    >>>format_tag('user:"foo bar"'')
    'user', 'foo bar'
    """
    idx = tag.index(":")
    key = tag[:idx].strip('"')
    value = tag[idx + 1 :].strip('"')
    return key, value