python os.path.join() 拼接时的坑

import os 

pwd = os.getcwd()

pwd1 = os.path.join(pwd,'/a')
pwd2 = os.path.join(pwd,'a')

print (pwd)
print (pwd1)
print (pwd2)

如果第二个参数中首字符时‘/’，拼接出来的链接不带第一个参数