python / python/mypy

dmypy only formats output in json the first time it's executed

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bug topic-daemon
Dominant language
Python
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Description

Bug Report

dmypy only outputs in json the first time it's invoked with --output=json.

To Reproduce

dmypy stop
dmypy run -- --output=json
dmypy run -- --output=json

Expected Behavior

Every invocation returns JSON.

Actual Behavior

Only the first one does.

$ dmypy run -- --output=json
Daemon started
{"file": "myfile.py", "line": 3, "column": 0, "message": "Function is missing a type annotation", "hint": null, "code": "no-untyped-def", "severity": "error"}

$ dmypy run -- --output=json
a_different_file.py:22: error: Missing type parameters for generic type "Query"  [type-arg]

Your Environment

mypy --version
mypy 1.15.0 (compiled: yes)

python --version
Python 3.11.11

Contributor guide

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Reproduce the behavior with the reported dmypy stop and repeated dmypy run -- --output=json commands, then trace the dmypy run output handling. Done means every invocation emits JSON rather than only the first one; no specific source file or test is named in the issue.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
cli, tooling
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
45/100

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