TypeError: __str__ returned non-string error

[jolinchewjb]

the result is : TypeError: __str__ returned non-string (type NoneType), but i think my __str__ function is correct,any idea? thanks, this is under python 3.5.1

class srvinfo(object):

def __init__(self,id,name=None,comp=None):
self.id=id
self.name=name

self.comp=comp

def change_usr(self,id,name,comp):
self.id=id
self.name=name
self.comp=comp

def __str__(self):

return f '{self.id} {self.name} : {self.comp}'
s=srvinfo(1021)
print(s)
s.change_usr(1022,'Jeffery','Microsoft')
print(s)

[jolinchewjb]

class srvinfo(object):

def __init__(self,id,name=None,comp=None):
self.id=id
self.name=name

self.comp=comp

def change_usr(self,id,name,comp):
self.id=id
self.name=name
self.comp=comp

def __str__(self):

return f '{self.id} {self.name} : {self.comp}' 
s=srvinfo(1021)
print(s)
s.change_usr(1022,'Jeffery','Microsoft')
print(s)

[buran]

Please, when post code, make sure indentation is preserved. As is at the moment it is non-sense.
Also, post full traceback in error tags.
Finally, based on trying to use f-strings, this code is intended for python version 3.6 or higher. It cannot run on 3.5.1.

[jolinchewjb]

my question is how to translate: return f '{self.id} {self.name} : {self.comp}' in Python 3.6.1 to Python 3.5.1, i have to use Python 3.5.1

[buran]

use format()

return '{} {} : {}'.format(self.id, self.name, self.comp)

[jolinchewjb]

thanks