file.write() Write string
Last updated: 2026-09-22
file.write() Write string
file.write(s) writes string s to the file; returns the number of characters written.
| Category | File Methods |
|---|---|
| Kind | Built-in Type Method |
| Python Version | all |
📝 Syntax
file.write()⚙️ Parameters
| s Required | The string (text mode) or bytes (binary mode) to write. |
|---|
Returns：int. The number of chars (text mode) or bytes (binary mode) written.
Mutates the original：No (returns a new object)
💥 Raises
TypeError— Raised when s is not a str or bytes.OSError— Raised when the file is read-only, closed, or the write fails.
▶ Example
Edit the code, press Run, and see the result in the output panel:
Output：
5💡 Related Cases
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❓ FAQ
QWhat does write() return?
AThe number of characters actually written (text mode) or bytes written (binary mode), which may be less than the length of the input.
QCan I write bytes in text mode?
ANo; text mode requires str, and writing bytes raises TypeError; binary mode is the opposite and requires bytes.
QDoes write() write to disk immediately?
ANot necessarily; the content first enters the buffer, and only close() or flush() guarantees it is written to disk.
QDoes writing overwrite or append?
AIt depends on the open mode: 'w' overwrites, 'a' appends. write() itself only writes at the current position.
