检查模型是否有开口边
思路：
跟重合点类似，只是这个要用到新的命令polyListComponentConversion，转换命令（比如选中边，到面，到点）
import maya.cmds as mc
sel = mc.ls(sl=True)
list_sel = []
for a in sel:
edge_num = mc.polyEvaluate(a,e=True)
for b in range(edge_num):
edge_name = '{}.e[{}]'.format(a,b)
edge_face = mc.polyListComponentConversion(edge_name,tf=True)
for c in edge_face:
if ':' in c:
pass
else:
if len(edge_face) == 1:
list_sel.append(edge_name)
mc.select(list_sel)
