[PR #8211/7725f5a2 backport][3.9] Fix type annotations on MultipartWriter.append

[patchback]

This is a backport of PR #8211 as merged into master (7725f5a).

What do these changes do?

They adjust the annotations on the MultipartWriter.append method (and two similar methods), so that type-checkers admit plain python dictionaries for the second argument; the headers parameter.

I chose to use LooseHeaders as I knew it was already used as the headers parameter for the web.Response constructor, among others. Changed to Mapping[str, str] , thank you Dreamsorcerer

Are there changes in behavior for the user?

No, this doesn't change any behaviour.

Is it a substantial burden for the maintainers to support this?

Not that I can imagine.

Related issue number

Fixes #7741

Checklist

• I think the code is well written
• Unit tests for the changes exist
  • I think the existing tests should be sufficient for seeing that the str and istr keyed dictionaries work with append

    • aiohttp/tests/test_multipart.py

      Line 1310 in d8936aa

      writer.append("hello, world!", {"x-foo": "bar"})

    • aiohttp/tests/test_multipart.py

      Line 1323 in d8936aa

      writer.append(part, {CONTENT_TYPE: "test/passed"})

      
      but am also open to suggestions
• Documentation reflects the changes
  • Documentation already gives examples

    • aiohttp/docs/multipart.rst

      Lines 145 to 146 in d8936aa

      	mpwriter.append(io.BytesIO(b'GIF89a...'),
      	{'CONTENT-TYPE': 'image/gif'})

• If you provide code modification, please add yourself to CONTRIBUTORS.txt
  • The format is <Name> <Surname>.
  • Please keep alphabetical order, the file is sorted by names.
• Add a new news fragment into the CHANGES/ folder

  • name it <issue_or_pr_num>.<type>.rst (e.g. 588.bugfix.rst)

  • if you don't have an issue number, change it to the pull request
    number after creating the PR

    • .bugfix: A bug fix for something the maintainers deemed an
      improper undesired behavior that got corrected to match
      pre-agreed expectations.
    • .feature: A new behavior, public APIs. That sort of stuff.
    • .deprecation: A declaration of future API removals and breaking
      changes in behavior.
    • .breaking: When something public is removed in a breaking way.
      Could be deprecated in an earlier release.
    • .doc: Notable updates to the documentation structure or build
      process.
    • .packaging: Notes for downstreams about unobvious side effects
      and tooling. Changes in the test invocation considerations and
      runtime assumptions.
    • .contrib: Stuff that affects the contributor experience. e.g.
      Running tests, building the docs, setting up the development
      environment.
    • .misc: Changes that are hard to assign to any of the above
      categories.

  • Make sure to use full sentences with correct case and punctuation,
    for example:

    Fixed issue with non-ascii contents in doctest text files
    -- by :user:`contributor-gh-handle`.

    Use the past tense or the present tense a non-imperative mood,
    referring to what's changed compared to the last released version
    of this project.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.36%. Comparing base (0153145) to head (4b07e13).

Additional details and impacted files

@@           Coverage Diff           @@
##              3.9    #8214   +/-   ##
=======================================
  Coverage   97.36%   97.36%           
=======================================
  Files         108      108           
  Lines       32637    32637           
  Branches     3874     3874           
=======================================
  Hits        31778    31778           
  Misses        655      655           
  Partials      204      204           

Flag	Coverage Δ
CI-GHA	97.27% <100.00%> (ø)
OS-Linux	96.96% <100.00%> (ø)
OS-Windows	94.47% <100.00%> (ø)
OS-macOS	96.58% <100.00%> (ø)
Py-3.10.11	94.37% <100.00%> (ø)
Py-3.10.13	96.75% <100.00%> (ø)
Py-3.11.8	96.47% <100.00%> (ø)
Py-3.12.2	96.52% <100.00%> (ø)
Py-3.8.10	94.35% <100.00%> (ø)
Py-3.8.18	96.68% <100.00%> (ø)
Py-3.9.13	94.36% <100.00%> (ø)
Py-3.9.18	96.73% <100.00%> (ø)
Py-pypy7.3.15	96.27% <100.00%> (ø)
VM-macos	96.58% <100.00%> (ø)
VM-ubuntu	96.96% <100.00%> (ø)
VM-windows	94.47% <100.00%> (ø)

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