File Methods

fileno()

Return the integer file descriptor used by the underlying operating system.

file.fileno()

file.fileno() returns the integer file descriptor assigned to the open file by the OS.

Returns

An integer representing the operating system file descriptor.

Run it and change it

import tempfile
with tempfile.NamedTemporaryFile(mode='w+', delete=True) as f:
    fd = f.fileno()
    print('Is integer FD:', isinstance(fd, int))

Low-level OS operations: File descriptors are used with the os module functions like os.read(), os.write(), and os.fstat().