def normalize(df, col_name, replace=True):
    """Normalize number column in DataFrame

    The normalization is done with max-min equation:
    z = (x - min(x)) / (max(x) - min(x))

    replace -- set to False if it's desired to return new DataFrame
               instead of editing it.
    """
    col = df[col_name]
    norm_col = (col - col.min()) / (col.max() - col.min())

    if replace:
        df[col_name] = norm_col
        return df
    else:
        norm_df = df.copy()
        norm_df[col_name] = norm_col
        return norm_df