Changing strings in files

[Manfred Lotz]

I have a situation where in a directory tree I want to change a certain
string in all files where that string occurs.

My idea was to do

- os.scandir and for each file
   - check if a file is a text file
   - if it is not a text file skip that file
   - change the string as often as it occurs in that file


What is the best way to check if a file is a text file? In a script I
could use the `file` command which is not ideal as I have to grep the
result. In Perl I could do  -T file.

How to do best in Python?

-- 
Thanks,
Manfred