Syntax error in Maya

I wouldn't normally post something so seemingly basic but I've been puzzling over this all afternoon. Maya is giving me a wonderfully non-specific 'Syntax error' whenever I try to run this code, can anyone see the issue?

import maya.cmds as cmds

def listSelMesh(*args):
    cmds.textScrollList("ab_meshList", en=1, ra=1)  #CLEAR THE OLD LIST
    trans = cmds.ls(sl=1)  #LIST SELECTED OBJECTS
    meshList = cmds.listRelatives(trans, c=1) or []  #GET ANY SHAPES
    shapeList = cmds.ls(meshList, t=1)  #GET ANY MESHES
    for trans in shapeList:
        cmds.textScrollList("ab_meshList", e=1, a=trans)  #APPEND THE CLEARED LIST WITH THE NEW SHAPES        

#Create the UI
def createUI(pWindowTitle, pApplyCallback):
    windowID = 'ba_skinExport'
    #If the UI is already open, delete the pre-existing instance
    if cmds.window(windowID, exists=True):
        cmds.deleteUI(windowID)
        
    cmds.window(windowID, title=pWindowTitle, sizeable=True, resizeToFitChildren=True)
        
    #Layout the columns in the UI
    cmds.columnLayout(adjustableColumn=True)
    form = cmds.formLayout()
    text1 = cmds.text(label='Selected mesh')
    shapeList = cmds.textScrollList("ab_meshList", p=form, h=75)
        
    btn1 = cmds.button(label='Load', command=listSelMesh)
    btn2 = cmds.button(label='Export', command=pApplyCallback)
    btn3 = cmds.button(label='Import', command=pApplyCallback)
    btn4 = cmds.button(label='Cancel', command=cancelCallback, w=85)
        
    cmds.showWindow()
        
    cmds.formLayout(form, e=1,
                    attachForm=((shapeList, "top", 10), (shapeList, "left", 100), (shapeList, "right", 10),
                                (btn1, "top", 92), (btn1, "left", 100), (btn1, "right", 10),
                                (text1, "top", 92), (text1, "left", 20),
                                (btn2, "top", 144), (btn2, "left", 100), (btn2, "right", 100),
                                (btn3, "top", 144), (btn3, "left", 100), (btn3, "right", 100),
                                (btn4, "top" 144), (btn4, "left", 10)
                    ))                    
                        
createUI('ba_skinExport', applyCallback)

Solution

Change this line,(missed a ,)

(btn4, "top" 144)

(btn4, "top", 144)