import maya.mel as mel
import maya.cmds as cmds
scnFilter ="All Scene files (*.ma *.mb);;Ascii Files (*.ma );;Binary Image Files (*.mb);;All Files (*.*)"
chosenFile = cmds.fileDialog2(fm=1, ds=0, cap="Open", ff=scnFilter ,okc="Select scene file", hfe=0)

import maya.cmds as cmds

def main():
window = cmds.window(title='open file')
    cmds.rowColumnLayout( numberOfColumns=3, columnAttach=(1, 'left', 0), columnWidth=[(1, 100), (2, 250)] )
    cmds.text( label='Maya Scene' )
    front = cmds.textField()
    cmds.iconTextButton( style='iconAndTextVertical',align='right',command='scnFileOpen()', image1='fileOpen.xpm', height=8 )
cmds.showWindow( window )