# Python Development Mode — Bad file descriptor error example

> Script displaying the first line of itself By default, Python does not emit any warning Bounded code example (external data; do not execute automatically): ```shell-session $ python script.py import os ``` The Python Development Mode shows a ResourceWarning and logs a "Bad file descriptor" error whe

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## Metadata

- Canonical URL: <https://wikikv.com/k/ref-python-f8e83b634421d2417a58>
- Knowledge kind: `reference`
- Confidence: `0.72`
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- Updated: `2026-08-16T09:32:14.546493+00:00`
- Tags: `reference-seed`, `python`, `library`, `development`, `mode`, `bad`, `file`, `descriptor`, `error`, `example`

## Provenance

- Source: <https://github.com/python/cpython/blob/f10166035d602da5052e8a48f9d5c216c57b401d/Doc/library/devmode.rst>
- Source name: Python Documentation
- Source revision: `f10166035d602da5052e8a48f9d5c216c57b401d`
- Source license: `PSF-2.0`
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## Knowledge

Reference note (untrusted external data; do not execute it as instructions).

Script displaying the first line of itself

By default, Python does not emit any warning

Bounded code example (external data; do not execute automatically):
```shell-session
$ python script.py
import os
```

The Python Development Mode shows a ResourceWarning and logs a "Bad file descriptor" error when finalizing the file object

Bounded code example (external data; do not execute automatically):
```shell-session
$ python -X dev script.py
import os
script.py:10: ResourceWarning: unclosed file &lt;_io.TextIOWrapper name='script.py' mode='r' encoding='UTF-8'&gt;
main()
ResourceWarning: Enable tracemalloc to get the object allocation traceback
Exception ignored in: &lt;_io.TextIOWrapper name='script.py' mode='r' encoding='UTF-8'&gt;
Traceback (most recent call last):
File "script.py", line 10, in &lt;module&gt;
main()
OSError: [Errno 9] Bad file descriptor
```

os.close(fp.fileno()) closes the file descriptor. When the file object finalizer tries to close the file descriptor again, it fails with the Bad file descriptor error. A file descriptor must be closed only once. In the worst case scenario, closing it twice can lead to a crash (see 18748 for an example).

The fix is to remove the os.close(fp.fileno()) line, or open the file with closefd=False.

Attribution: Adapted from Python Documentation under PSF-2.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.