“Can only join an iterable” python error

问题

I've already looked at this post about iterable python errors:

"Can only iterable" Python error

But that was about the error "cannot assign an iterable". My question is why is python telling me:

 "list.py", line 6, in <module>
    reversedlist = ' '.join(toberlist1)
TypeError: can only join an iterable

I don't know what I am doing wrong! I was following this thread:

Reverse word order of a string with no str.split() allowed

and specifically this answer:

>>> s = 'This is a string to try'
>>> r = s.split(' ')
['This', 'is', 'a', 'string', 'to', 'try']
>>> r.reverse()
>>> r
['try', 'to', 'string', 'a', 'is', 'This']
>>> result = ' '.join(r)
>>> result
'try to string a is This'

and adapter the code to make it have an input. But when I ran it, it said the error above. I am a complete novice so could you please tell me what the error message means and how to fix it.

Code Below:

import re
list1 = input ("please enter the list you want to print")
print ("Your List: ", list1)
splitlist1 = list1.split(' ')
tobereversedlist1 = splitlist1.reverse()
reversedlist = ' '.join(tobereversedlist1)
yesno = input ("Press 1 for original list or 2 for reversed list")
yesnoraw = int(yesno)
if yesnoraw == 1:
    print (list1)
else:
    print (reversedlist)

The program should take an input like apples and pears and then produce an output pears and apples.

Help would be appreciated!

回答1:

splitlist1.reverse(), like many list methods, acts in-place, and therefore returns None. So tobereversedlist1 is therefore None, hence the error.

You should pass splitlist1 directly:

splitlist1.reverse()
reversedlist = ' '.join(splitlist1)

回答2:

string join must satisfy the connection object to be iterated(list, tuple)

splitlist1.reverse() returns None, None object not support iteration.

来源：https://stackoverflow.com/questions/32144173/can-only-join-an-iterable-python-error