ENH: .merge - specify string literals for .merge how keyword

[alexcolemandata]

Feature Type

• Adding new functionality to pandas

• Changing existing functionality in pandas

• Removing existing functionality in pandas

Problem Description

The how keyword for DataFrame.merge is typed as a string - which means that type checkers can miss potential errors, as it only accepts a subset of strings ("inner", "outer", "left", "right", "cross").

Feature Description

pandas._typing : add a MergeHow type, specifying the string literals that how accepts

pandas.core.frame: how as accepting an argument of type MergeHow

Alternative Solutions

Alternatively we could specify the string literals in the merge method function header

Additional Context

Related PR for pandas-stubs

[alexcolemandata]

take

[phofl]

Hi, thanks for your report. You'll have to add this here and in the stubs repo. Otherwise it won't get picked up by type checkers