file.fileno() File descriptor
Last updated: 2026-09-22
file.fileno() File descriptor
file.fileno() returns the integer file descriptor used by the OS.
| Category | File Methods |
|---|---|
| Kind | Built-in Type Method |
| Python Version | all |
📝 Syntax
file.fileno()Returns：int. The OS-level integer file descriptor.
Mutates the original：No (returns a new object)
💥 Raises
OSError— Raised when the file is closed or the stream has no file descriptor.
▶ Example
Edit the code, press Run, and see the result in the output panel:
Output：
True💡 Related Cases
More case studies coming soon — check back later.
❓ FAQ
QWhat does fileno() return?
AThe OS-level integer file descriptor, used for low-level operations such as select and os.read.
QWhat happens when called after the file is closed?
AAn OSError is raised (the file is closed, or the stream has no file descriptor).
QWhen is it used?
AWhen passing the file object to libraries that need an fd (such as select and socket-related operations).
