code:
import wx

import matplotlib

matplotlib.use( 'WXagg' )

from matplotlib.backends.backend_wxagg import FigureCanvasWxAgg
from matplotlib.figure import Figure

class BarChartBandwidthHistory( FigureCanvasWxAgg ):
	def __init__( self, parent, monthly_usage ):
		divisor = 1.0
		unit = 'B'

		highest_usage = max( ( m[1] for m in monthly_usage ) )

		lines = [ ( 1073741824.0, 'GB' ), ( 1048576.0, 'MB' ), ( 1024.0, 'KB' ) ]

		for ( line_divisor, line_unit ) in lines:
			if highest_usage > line_divisor:
				divisor = line_divisor
				unit = line_unit

				break

		monthly_usage = [ ( month_str, month_value / divisor ) for ( month_str, month_value ) in monthly_usage ]

		( r, g, b, a ) = wx.SystemSettings.GetColour( wx.SYS_COLOUR_FRAMEBK ).Get()

		facecolor = '#{:0>2x}{:0>2x}{:0>2x}'.format( r, g, b )

		figure = Figure( figsize = ( 6.4, 4.8 ), dpi = 80, facecolor = facecolor, edgecolor = facecolor )

		axes = figure.add_subplot( 111 )

		x_indices = list( range( len( monthly_usage ) ) )

		axes.bar( x_indices, [ i[1] for i in monthly_usage ] )

		axes.set_xticks( x_indices )
		axes.set_xticklabels( [ i[0] for i in monthly_usage ] )

		axes.grid( True )
		axes.set_axisbelow( True )

		axes.set_ylabel( '(' + unit + ')' )

		axes.set_title( 'historical usage' )

		FigureCanvasWxAgg.__init__( self, parent, -1, figure )