Copying a file to an existing directory results in IOError [Error 21] is a directory

You're using the wrong function. You might want "copy":

https://docs.python.org/2/library/shutil.html

You have already answered yourself in the question.

dst should be the path to the copied file. So if you want to copy the file to /var/lib/my/ and your file is called f1 then dst should be /var/lib/my/f1.txt

Try to use shutil.copy as suggested here by john-estess

shutil.copy(src, dst)

or try to fix this using the following snippet

shutil.copyfile(src, '%s/%s' % (dst, src.split('/')[-1]))

Assuming src is the path of the file you want to copy, such as /var/log/apache/access.log, and dst is the path to the directory, where you want to copy the file, for example, /var/lib/my then the new destination is /var/lib/my/access.log.