def convertVariableName(variable):
    """
    Return the mixedCase version of a SERPENT variable.

    Parameters
    ----------
    variable: str
        ``SERPENT_STYLE`` variable name to be converted

    Returns
    -------
    str:
        Variable name that has been split at underscores and
        converted to ``mixedCase``

    Examples
    --------
    ::

        >>> v = "INF_KINF"
        >>> convertVariableName(v)
        infKinf

        >>> v = "VERSION"
        >>> convertVariableName(v)
        version

    """
    lowerSplits = [item.lower() for item in variable.split('_')]
    if len(lowerSplits) == 1:
        return lowerSplits[0]
    return lowerSplits[0] + ''.join([item.capitalize()
                                     for item in lowerSplits[1:]])