update pd.DataFrame.merge - add typing for how parameter

[alexcolemandata]

• closes ENH: .merge - specify string literals for .merge how keyword #48503
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

[alexcolemandata]

PR for pandas-stubs: pandas-dev/pandas-stubs#289

[phofl]

Thx, can you add this for join too? Additionally, I think we are typing how internally too, would be great to add this there too

[twoertwein]

Thx, can you add this for join too? Additionally, I think we are typing how internally too, would be great to add this there too

For DataFrame.join, you probably need MergeHow | Literal["cross"].

Could also use MergeHow in Index.join/_join* (in pandas/core/indexes/base.py) and for the align methods NDFrame/DataFrame/Series.align (in pandas/core/{generic,frame,series}.py)

[phofl]

MergeHow includes cross already?

[twoertwein]

MergeHow includes cross already?

You are right :) Forget about my comment :)

[github-actions]

This pull request is stale because it has been open for thirty days with no activity. Please update and respond to this comment if you're still interested in working on this.

[mroeschke]

Thanks for the pull request, but it appears to have gone stale. If interested in continuing, please merge in the main branch, address any review comments and/or failing tests, and we can reopen.