DKRZ PyNGL example bar chart

Example:

import numpy as np
import Ngl

#-- function get_bar returns coordinates of a bar
def get_bar(x,y,dx,ymin,bar_width_perc=0.6):
    dxp = (dx * bar_width_perc)/2.
    xbar = np.array([x-dxp, x+dxp, x+dxp, x-dxp, x-dxp])
    ybar = np.array([ ymin, ymin, y, y, ymin])
    return xbar,ybar

#-----------------------------------------------------------------------
#-- Function: main
#-----------------------------------------------------------------------
def main():

    #-- create random x- and y-values
    x = np.arange(1,13,1)
    y = [8,5,11,6,9,9,6,2,4,1,3,3]
    dx = min(x[1:-1]-x[0:-2]) #-- distance between x-values

    #-- define color and x-axis labels
    color = 'blue'
    xlabels = ["Jan","Feb","Mar","Apr","May","Jun", \
               "Jul","Aug","Sep","Oct","Nov","Dec"]#-- x-axis labels

    #-- open a workstation
    wkres = Ngl.Resources() #-- generate an resources object for workstation
    wks_type = "png" #-- output type of workstation
    wks = Ngl.open_wks(wks_type,"plot_TRANS_bar_chart_py",wkres)

    #-- set resources
    res = Ngl.Resources() #-- generate an res object for plot
    res.nglFrame = False #-- don't advance frame
    res.nglPointTickmarksOutward = True #-- point tickmarks outward

    res.tiXAxisString = "x-values" #-- x-axis title
    res.tiYAxisString = "y-values" #-- y-axis title

    res.tmXBMode = "Explicit" #-- define bottom x-axis values and labels
    res.tmXBValues = x #-- x-axis values
    res.tmXBLabels = xlabels #-- x-axis labels
    res.tmXBLabelFontHeightF = 0.012 #-- bottom x-axis font size

    res.trXMinF = 0.0 #-- x-axis min value
    res.trXMaxF = 13.0 #-- x-axis max value
    res.trYMinF = 0.0 #-- y-axis min value
    res.trYMaxF = 12.0 #-- y-axis max value

    #-- bar resources
    barres = Ngl.Resources() #-- resource list for bars
    barres.gsFillColor = color #-- set bar color

    #-- loop through each y point and create bar
    for i in range(len(y)):
        xbar,ybar = get_bar(x[i], y[i], dx, res.trXMinF, 0.3)
        plot = Ngl.xy(wks, xbar, ybar, res)
        Ngl.polygon(wks, plot, xbar, ybar, barres) #-- filled bar

    Ngl.frame(wks) #-- advance frame
    Ngl.end()

if __name__ == '__main__':
    main()

Result: