I m working on a python project currently, It is a application which don not interact with internet.GUI is being dine with wxpython. Is there code available in python which can simulate button click.
I depends on what you really need it to do.  Do you just want cause the same code to be executed as would be done when the user clicks the button?  Or do you need to have a real system level mouse event occur on the native UI button as if there was a real user doing it?
For the former you just need to cause the event handler function to be called from wherever you need it to be done.  You can create a matching event object and use wx.PostEvent as suggested, or simply call the event handler method directly.  Or for a little bit better programming style, refactor and move the guts of the event handler to a separate function and call it from the event handler and also wherever else you need to simulate the effects of clicking the button.
For having real system level events being sent to the native widget there is the wx.UIActionSimulator class, which can be used to simulate the mouse or keyboard at a lower level than posting wx events, so the UI behaves exactly the same as if there was a real user doing it.  I would guess that 95% of the time that this is overkill for cases like what you describe, and also more complex than the above, but it's there if you really need it.
simulating button click in python