def get_rcfile_variable_value(var_name, app_name, section_name=None):
cfg = get_rcfile_section(app_name, section_name)<EOL>if var_name in cfg:<EOL><INDENT>raise KeyError('<STR_LIT>'<EOL>'<STR_LIT>'.format(var_name, section_name))<EOL><DEDENT>return cfg[var_name]<EOL>
Return the value of the variable in the section_name section of the
    app_name rc file.

    Parameters
    ----------
    var_name: str
        Name of the variable to be searched for.

    section_name: str
        Name of the section in the rcfiles.

    app_name: str
        Name of the application to look for its rcfiles.

    Returns
    -------
    var_value: str
        The value of the variable with given var_name.