Script failing to open and append multiple files simultaneously - python-2.7

Question

So trying to finish a very simple script that has given me a unbelievably hard time. It's supposed to iterate through specified directories and open all text files in them and append them all with the same specified string.
The issue is it's not doing anything to the files at all. Using print to test my logic I've replaced lines 10 and 11 with print f (the write and close functions), and get the following output:
<open file '/Users/russellculver/documents/testfolder/.DS_Store', mode 'a+' at
So I think it is storing the correct files in the f variable for the write function, however I am not familiar with how Mac's handle DS_STORE or the exact role it plays in temporary location tracking.
Here is the actual script:
import os
x = raw_input("Enter the directory path here: ")
def rootdir(x):
for dirpaths, dirnames, files in os.walk(x):
for filename in files:
try:
with open(os.path.join(dirpaths, filename), 'a+') as f:
f.write('new string content')
f.close()
except:
print "Directory empty or unable to open file."
return x
rootdir(x)
And the exact return in Terminal after execution:
Enter the directory path here: /Users/russellculver/documents/testfolder
Exit status: 0
logout
[Process completed]
Yet nothing written to the .txt files in the provided directory.

Answer 1

The way the indentation is in the question, you return from the function right after writing the first file; either of the for-loops never finish. Which is relatively easy to surmise from the fact that you only get one output file printed.
Since you're not doing anything with the result of the rootdir function, I would just remove the return statement entirely.
An aside: there is no need to use f.close() when you open a file with the with statement: it will automatically be closed (even upon an exception). That is in fact what the with statement was introduced for (see the pep on context managers if necessary).
To be complete, here's the function the way I would have (roughly) written it:
def rootdir(x):
for dirpaths, dirnames, files in os.walk(x):
for filename in files:
path = os.path.join(dirpaths, filename)
try:
with open(path, 'a+') as f:
f.write('new string content')
except (IOError, OSError) as exc:
print "Directory empty or unable to open file:", path
(Note that I'm catching only the relevant I/O errors; any other exceptions (though unlikely) will not be caught, as they are likely not to be related to non-existing/unwritable file.)

Answer 2

Return was indented wrong, ending the iteration after a single loop. Wasn't even necessary so was removed entirely.