lchmod is one of a number of os functions that is not available on older versions of macOS.  Chances are you are using a Python binary (possibly one supplied by a python.org installer) that was built to be used on a range of macOS versions and the oldest version did not support lchmod.  Note that there is a general warning about interface availability in the documentation for the os module:

"An “Availability: Unix” note means that this function is commonly found on Unix systems. It does not make any claims about its existence on a specific operating system."

Either use a version of Python built only for the latest versions of macOS or add a test in your code for the availability of lchown.

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