function <property_name>_<parameter_name>_OnButtonClicked()
{
...
}

def <property_name>_<parameter_name>_OnButtonClicked():
                                ...

Function <property_name>_<parameter_name>_OnButtonClicked()
                                ...
End Function

sub <property_name>_<parameter_name>_OnButtonClicked
{ 
        ... 
}

import win32com.client
from win32com.client import constants

def XSILoadPlugin( in_reg ):
        in_reg.Author = "Autodesk"
        in_reg.Name = "MyPropertyPlugin"
        in_reg.Major = 1
        in_reg.Minor = 0

        in_reg.RegisterProperty("MyProperty")
        #RegistrationInsertionPoint - do not remove this line

        return True

def XSIUnloadPlugin( in_reg ):
        strPluginName = in_reg.Name
        return True

def MyProperty_Define( in_ctxt ):
        oCustomProperty = in_ctxt.Source
        oCustomProperty.AddGridParameter("MyGrid")
        return True

def MyProperty_DefineLayout( in_ctxt ):
        oLayout = in_ctxt.Source
        oLayout.Clear()
        oItem = oLayout.AddItem("MyGrid")
        return True

def MyProperty_OnInit( ):
        Application.LogMessage("MyProperty_OnInit called",constants.siVerbose)
        param = PPG.MyGrid

        # Basic population of the grid data
        gridData = param.Value
        gridData.ColumnCount = 3
        gridData.RowCount = 3
        
        for col in range( gridData.ColumnCount ):
                gridData.SetColumnLabel( col, "Col %d"%col )
                gridData.SetColumnDef( col, constants.siColumnButton )
                for row in range( gridData.RowCount ):
                        if col == 0:
                                gridData.SetRowLabel( row, "Row %d"%row )
                        gridData.SetCell( col, row, "%d,%d"%(col, row) )

def MyProperty_OnClosed( ):
        pass

def MyProperty_MyGrid_OnButtonClicked( in_ExtraParams ):
        param = PPG.MyGrid
        gridData = param.Value
        
        # Retrieve the set of cells on which a button was clicked
        # (if multiple "button" cells are selected prior to clicking 
        # then all the cells are part of the callback extra parameters)
        columnRowPairs = []
        columnRowPairs.extend( in_ExtraParams[0] )
        
        logString = "Button clicked on these cells: "
        while len( columnRowPairs ) >= 2:
                col = columnRowPairs.pop(0)
                row = columnRowPairs.pop(0)

                logString += "(%d, %d), "%(col, row)

        Application.LogMessage( logString )