How to check if two directories or files belong to same filesystem

Question

What's the best way to check if two directories belong to the same filesystem?

Acceptable answers: bash, python, C/C++.

Answer 1

It can be done by comparing device numbers.

In a shell script on Linux it can be done with stat:

stat -c "%d" /path  # returns the decimal device number 

In python:

os.lstat('/path...').st_dev

or

os.stat('/path...').st_dev

Answer 2

The standard command df shows on what filesystem the specified file(s) is located.

if df -P -- "$1" "$2" | awk 'NR==2 {dev1=$1} NR==3 {exit($1!=dev1)}'; then
  echo "$1 and $2 are on the same filesystem"
else
  echo "$1 and $2 are on different filesystems"
fi