def camel_case(string):
    """
    Converts a string to camel case. For example::

        camel_case('one_two_three') -> 'oneTwoThree'
    """
    if not string:
        return string
    parts = snake_case(string).split('_')
    rv = ''
    while parts:
        part = parts.pop(0)
        rv += part or '_'
        if part:
            break
    return rv + ''.join(x.title() for x in parts)