Python 为什么def定义之后，还是显示未定义呢？

Question

def transfer(s):
 s1=time.strftime('%Y-%m-%d%H:%M:%S'/time.localtime(int(s)))
s2=pd.Series(pd.to_datetime(s1)).dt.year.item()
if s2>=2000:
 s2='00'
elif s2>=1990:
 s2='90'
elif s2>=1980:
 s2='80'
else:
 s2='70'
return s2

Answer 1

程序不仅格式不对，函数strftime也是错的

def transfer(s):
  s1=time.strftime('%Y-%m-%d%H:%M:%S',time.localtime(int(s)))
  s2=pd.Series(pd.to_datetime(s1)).dt.year.item()
  if s2>=2000:
     s2='00'
  elif s2>=1990:
     s2='90'
  elif s2>=1980:
     s2='80'
  else:
    s2='70'
  return s2