def df_string(df, percentage_columns=(), format_map=None, **kwargs):
    """Return a nicely formatted string for the given dataframe.

    Arguments
    ---------
    df : pandas.DataFrame
        A dataframe object.
    percentage_columns : iterable
        A list of cloumn names to be displayed with a percentage sign.

    Returns
    -------
    str
        A nicely formatted string for the given dataframe.

    Example
    -------
    >>> import pandas as pd
    >>> df = pd.DataFrame([[8,'a'],[5,'b']],[1,2],['num', 'char'])
    >>> print(df_string(df))
       num char
    1    8    a
    2    5    b
    """
    formatters_map = {}
    for col, dtype in df.dtypes.iteritems():
        if col in percentage_columns:
            formatters_map[col] = '{:,.2f} %'.format
        elif dtype == 'float64':
            formatters_map[col] = '{:,.2f}'.format
    if format_map:
        for key in format_map:
            formatters_map[key] = format_map[key]
    return df.to_string(formatters=formatters_map, **kwargs)