python pandas implementations of spread and gather dplyr verbs

spread_gather.py

def gather( df, key, value, cols ):
    id_vars = [ col for col in df.columns if col not in cols ]
    id_values = cols
    var_name = key
    value_name = value
    return pd.melt( df, id_vars, id_values, var_name, value_name )

def spread( df, index, columns, values ):
    return df.pivot(index, columns, values).reset_index(level=index).rename_axis(None,axis=1)