how to put gap between y axis and first bar in vertical barchart matplotlib

I have a barchart code snippet as below..When you run this,you get 4 bars ,the first of which lies against the y axis.Is it开发者_StackOverflow社区 possible to put some gap between y axis and the first bar?

def plot_graph1():
    xvals = range(4)
    xnames=["one","two","three","four"]
    yvals = [10,30,40,20]
    width = 0.25
    yinterval = 10
    figure = plt.figure()
    plt.grid(True)
    plt.xlabel('x vals')
    plt.ylabel('y vals')
    plt.bar(xvals, yvals, width=width)
    plt.xticks([ x+(width/2) for x in  xvals],[x for x in xnames])
    plt.yticks(range(0,max(yvals),yinterval))
    figure.savefig("barchart.png",format="png")
    plt.show()
if __name__=='__main__':    
    plot_graph1()

The output is as below

Any help appreciated

thanks

mark

In your specific case, it's easiest to use plt.margins and plt.ylim(ymin=0). margins will act like axis('tight'), but leave the specified percentage of "padding", instead of scaling to the exact limits of the data.

Also, plt.bar has an align="center" option that simplifies your example somewhat.

Here's a slightly simplified version of your example above:

import matplotlib.pyplot as plt

def plot_graph1():
    xvals = range(4)
    xnames=["one","two","three","four"]
    yvals = [10,30,40,20]
    width = 0.25
    yinterval = 10

    figure = plt.figure()
    plt.grid(True)
    plt.xlabel('x vals')
    plt.ylabel('y vals')

    plt.bar(xvals, yvals, width=width, align='center')
    plt.xticks(xvals, xnames)
    plt.yticks(range(0,max(yvals),yinterval))
    plt.xlim([min(xvals) - 0.5, max(xvals) + 0.5])

    figure.savefig("barchart.png",format="png")
    plt.show()

if __name__=='__main__':    
    plot_graph1()