<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def read_dataset(dname):
 """Read example datasets. Parameters dname : string Name of dataset to read (without extension). Must be a valid dataset present in pingouin.datasets Returns ------- data : pd.DataFrame Dataset Examples -------- Load the ANOVA dataset """

    # Check extension
    d, ext = op.splitext(dname)
    if ext.lower() == '.csv':
        dname = d
    # Check that dataset exist
    if dname not in dts['dataset'].values:
        raise ValueError('Dataset does not exist. Valid datasets names are',
                         dts['dataset'].values)
    # Load dataset
    return pd.read_csv(op.join(ddir, dname + '.csv'), sep=',')