Preview the command formed by find -exec

You can do:

find . -exec ./is_dir.py {} \; -o -print

It will list everything that is not a directory. Assuming that is_dir.py is executable (chmod +x is_dir.py) and contains something like:

#!/usr/bin/env python

import sys
import os

if os.path.isdir(sys.argv[1]):
    sys.exit(0)
sys.exit(1)

And if is_dir.py generates output of its own, you can do:

 rm -f nondir.lst
 find . -exec ./is_dir.py {} \; -o -exec echo  {} >> nondir.lst \;

so that its outoput doesn't get mixed with the list of names for which is_dir.py fails.

If you run this command your touch file will be run, potentially multiple times, from the directory in which the command has been started:

find -name '*.pdf' -exec touch file \;

On the other hand, if you run this variant, each instance of the command will be run in the target file's directory:

find -name '*.pdf' -execdir touch file \;

In both cases you can see this in action by substituting the touch file with either echo {} and/or pwd.

From manpage:

-execdir command ;
-execdir command {} +

Like -exec, but the specified command is run from the subdirectory containing the matched file, which is not normally the directory in which you started find.