Output to stdout only if currently being redirected with > or >>

redirect.py

from os import fstat
from stat import S_ISREG

def is_redirected() -> bool:
    '''Detect if program is being redirected (i.e. using the > or >> operator).'''
    return S_ISREG(fstat(1).st_mode)

if __name__ == '__main__':
    if is_redirected():
        print('Hi file!')

redirect_only.sh

$ python redirect.py
$ python redirect.py | cat
$ python redirect.py > e.txt && cat e.txt
Hi file!