TypeError: 'function' object is not iterable

import os

def wenjian(file):
for root,dirs,files in os.walk(file):
for file in files:
filename = os.path.join(root,file)
print (filename[-28:])
return wenjian

PS C:\Users\ZHEN YUAN> & python "c:/Users/ZHEN YUAN/Desktop/第一步/wen2.py"
\Desktop\try\C2002455.xlsx
Traceback (most recent call last):
File "c:/Users/ZHEN YUAN/Desktop/第一步/wen2.py", line 14, in
for i in Names:
TypeError: 'function' object is not iterable

https://blog.csdn.net/xzy5210123/article/details/81067110