setting y-axis limit in matplotlib

Try this . Works for subplots too .
axes = plt.gca()
axes.set_xlim([xmin,xmax])
axes.set_ylim([ymin,ymax])

Another workaround is to get the plot’s axes and reassign changing only the y-values:
x1,x2,y1,y2 = plt.axis()
plt.axis((x1,x2,25,250))