[issue39400] pydoc: Use of MANPAGER variable is incorrect

[Ronan Pigott]

Ronan Pigott  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 _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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[issue39400] pydoc: Use of MANPAGER variable is incorrect

[Cheryl Sabella]

Change by Cheryl Sabella :


--
nosy: +serhiy.storchaka
versions: +Python 3.9 -Python 3.8

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[issue39400] pydoc: Use of MANPAGER variable is incorrect

[Roundup Robot]

Change by Roundup Robot :


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keywords: +patch
pull_requests: +17510
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/18123

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[issue39400] pydoc: Use of MANPAGER variable is incorrect

[Ronan Pigott]

Ronan Pigott  added the comment:

Actually my previous comment is incorrect, the value of the PAGER is split with 
the shell as a result of shell=True. There _is_ still an incompatibility with 
man.

I have a value for MANPAGER set like 'env LESS_TERMCAP_mb=^[[01;31m ... less' 
which becomes split on ';' by the shell as a result of 'shell=True'. The 
MANPAGER value is not interpreted by a shell with man, so it works as expected 
when using man.

Becuase man explicitly allows the use of quotes, it is possible to set a value 
of MANPAGER that has the desired effect for both programs by quoting the 
terminal control sequences like so: 'env LESS="^[[01;31m ... less"'.

Still, it might be reasonable to change pydocs interpretation of MANPAGER to 
better align with man's.

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[issue39400] pydoc: Use of MANPAGER variable is incorrect

[Ronan Pigott]

New submission from Ronan Pigott :

pydoc references the value of both MANPAGER and PAGER variables when selecting 
a command to present the user with documentation. Those values are passed 
directly to subprocess.Popen. However, MANPAGER may contain arguments that need 
splitting, and is explicitly documented as such in the `man 1 man` manpage:

> If $MANPAGER or $PAGER is set ($MANPAGER is used in preference), its value is 
> used as the name of the program used to display the manual page. [...] The 
> value may be a simple command name or a command with arguments, and may  use  
> shell quoting (backslashes,  single quotes, or double quotes). It may not use 
> pipes to connect multiple commands; if you need that, use a wrapper script 
> [...]

pydoc should perform word splitting a la shlex.split on the values of MANPAGER 
and PAGER to retain compatibility with man.

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components: Library (Lib)
messages: 360332
nosy: Brocellous
priority: normal
severity: normal
status: open
title: pydoc: Use of MANPAGER variable is incorrect
type: enhancement
versions: Python 3.8

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