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Negative run-time reported by subprocess.run's TimeoutExpired exception when setting timeout=0 #133089

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vadimkantorov opened this issue Apr 28, 2025 · 1 comment · May be fixed by #133103
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Negative run-time reported by subprocess.run's TimeoutExpired exception when setting timeout=0 #133089

vadimkantorov opened this issue Apr 28, 2025 · 1 comment · May be fixed by #133103
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3.13 bugs and security fixes 3.14 new features, bugs and security fixes stdlib Python modules in the Lib dir topic-subprocess Subprocess issues. type-bug An unexpected behavior, bug, or error

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@vadimkantorov
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vadimkantorov commented Apr 28, 2025 •
edited by bedevere-app bot
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Bug report

Bug description:

import subprocess
subprocess.run(['echo', 'hi'], timeout = 0)

# subprocess.TimeoutExpired: Command '['echo', 'hi']' timed out after -0.00010189996100962162 seconds
# subprocess.TimeoutExpired: Command '['echo', 'hi']' timed out after -4.819990135729313e-05 seconds

This is quite unexpected that the measured run-time can be negative

In general, it's unclear in the docs what behavior should have timeout=0. I would propose that it should disable timeout control, and should be equivalent to timeout=None.

But in any case, negative run-times are quite strange :)

CPython versions tested on:

3.12

Operating systems tested on:

WSLv1+Ubuntu24.04

Linked PRs
@vadimkantorov vadimkantorov added the type-bug An unexpected behavior, bug, or error label Apr 28, 2025
@picnixz picnixz added stdlib Python modules in the Lib dir topic-subprocess Subprocess issues. labels Apr 28, 2025
Zheaoli added a commit to Zheaoli/cpython that referenced this issue Apr 28, 2025
@Zheaoli
pythongh-133089: Make subprocess.run's behavior is same with 'timeo…
bfc8c24 
…ut=None' when the timeout is zero

Signed-off-by: Manjusaka <me@manjusaka.me>
@Zheaoli Zheaoli linked a pull request Apr 28, 2025 that will close this issue
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@vadimkantorov
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Btw, even outside of unspecified behavior for timeout=0, setting timeout to a very small value also prints negative time measurement:

import subprocess
subprocess.run(['echo', 'hi'], timeout = 1e-9)

# subprocess.TimeoutExpired: Command '['echo', 'hi']' timed out after -2.162200007660431e-05 seconds

How can time measurement be negative? Is it indicative of some other bug related to execution time measurement?

@ZeroIntensity ZeroIntensity added 3.13 bugs and security fixes 3.14 new features, bugs and security fixes labels May 1, 2025
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3.13 bugs and security fixes 3.14 new features, bugs and security fixes stdlib Python modules in the Lib dir topic-subprocess Subprocess issues. type-bug An unexpected behavior, bug, or error
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