[issue39400] pydoc: Use of MANPAGER variable is incorrect

[Ronan Pigott]

Ronan Pigott <rpigott at berkeley.edu> added the comment:

Any reason a change like this could not be added to a 3.8.x release?

Like I pointed out in the PR, pydoc's use of MANPAGER is undocumented and, as far as I'm concerned, incorrect.

A lot of software references idiosyncratic <PROGRAM>_PAGER vars, but pydoc reuses MANPAGER instead of something like PYDOC_PAGER. I don't think it's such a bad idea to reuse MANPAGER considering the two programs serve a similar function, but I think matching man's interpretation of MANPAGER is then the only reasonable behavior pydoc can take. If it does not, pydoc is by-default broken on plenty of otherwise fine setups.

As it stands, pydoc is broken _because_ of undocumented behavior. A user reading the docs carefully still might not recognize that pydoc is preferring their MANPAGER value over PAGER. For that reason, I'd call this a bugfix. The bug here could be considered that pydoc references MANPAGER _at all_. However, given what I think is the intent of the original code - to allow pydoc to benefit from a user's MANPAGER customization - I've tried to update pydoc to reflect that intent in the PR, rather than remove the feature.

I think this change could be eligible for 3.8.x. Thoughts?

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<https://bugs.python.org/issue39400>
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